The World’s Strangest Sound: Scientists May Have Finally Explained “The Hum”

Published: 25 Jul 2026

For fifty years, a small fraction of people around the world have heard a deep, droning noise that no one else can detect — and no microphone could ever quite catch. A new study out of Norway suggests the source may not be outside their homes at all, but inside their own ears.

Somewhere between 2 and 4 percent of people on Earth have heard it: a low, steady drone that seems to come from everywhere and nowhere at once. It slips in at night, right when the house goes quiet. It sounds like a truck idling down the street, or a generator running in a neighbor’s basement — except when you go outside to find it, there’s nothing there.

Family members sleeping in the same room often hear nothing at all.

For the people who do hear it, the sound is rarely just an annoyance. Some describe headaches, sleep loss, and a low-grade sense of dread that builds over months or years. Others describe something stranger still: a vibration they can feel in their chest or their teeth, as if the sound has weight. It has a name, and that name is simply The Hum.

For half a century, The Hum has defied nearly every attempt to pin it down. Investigators have brought in seismographs, military-grade microphones, and government scientists. They have shut down factories, silenced power lines, and driven trucks in circles looking for the source. Almost every time, the sound has slipped away from them.

Now, a team of hearing researchers at the Norwegian University of Science and Technology (NTNU), led by audiology professor Markus Drexl, has published a new study in the journal PLOS One that takes a very different approach. Instead of chasing the sound outward — into the environment — they turned their instruments inward, onto the people who hear it. What they found doesn’t hand The Hum’s believers a smoking gun. But it may be the closest thing to a real answer this mystery has had in fifty years.

The Phenomenon: What “The Hum” Actually Is

The Hum is not one single, agreed-upon sound. It’s an umbrella term for a class of experiences that share a few features:

A persistent, low-pitched droning, buzzing, or rumbling noise
Most noticeable indoors, and especially at night, when background noise drops away
Undetectable — or nearly undetectable — to standard microphones and to most other people nearby
Reported far more often by some individuals than others, even within the same household

Researchers estimate roughly 2-4 percent of people worldwide experience this unusual sound. For some hearers it’s a background irritation. For others, the low-frequency sound can cause physical discomfort or illness and may also feel like a vibration moving through the body. And in a detail that has puzzled investigators for decades, other people in the same room may hear nothing at all.

Because the sound sits at such a low frequency, it behaves differently than ordinary noise. As Drexl explains it, long, low-frequency sound waves can travel great distances, which is part of what makes them so hard to trace back to a single source — the ear that hears them struggles to tell which direction they’re coming from.

The Timeline: A Fifty-Year Mystery

Mid-1970s — Bristol, England. The first well-documented wave of complaints arrived at a local newspaper, the Bristol Evening Post, which began receiving a stream of letters from residents who described hearing an unexplained sound and wanted to know what was producing it. Investigators initially suspected large industrial fans operating inside a department store warehouse — but the complaints kept coming even after the warehouse closed several years later.

Late 1970s–1980s — Spreading across the UK. Reports followed in other British towns and cities, including Hythe, Plymouth, Southampton and Swansea, as well as London, cementing “The Hum” as a recognized, if unsolved, phenomenon in Britain.

Early 1990s — Taos, New Mexico, USA. The Hum crossed the Atlantic into American headlines when residents of the small artist town of Taos began reporting a persistent low drone. The complaints grew loud enough that in 1993 the New Mexico congressional delegation commissioned a formal, multi-institution investigation, bringing in researchers from Los Alamos National Laboratory, Sandia National Laboratories, the Phillips Air Force Laboratory, and the University of New Mexico, led by engineering professor emeritus Joe Mullins. The team monitored acoustic, seismic, and electromagnetic activity around the town. Despite active complaints during the monitoring window, the investigators found no unusual acoustic or seismic source they could point to as the cause — although some elevated electromagnetic readings were noted near power lines, with no proven link to the hum itself.

1990s — Kokomo, Indiana, USA. A second American hotspot emerged, this one eventually traced, at least partially, to industrial noise sources in the city — an outcome that stood in contrast to Taos, where no clear culprit was ever confirmed.

2000s–2010s — A truly global pattern. Reports kept surfacing far beyond the UK and the US: in Canada (notably the “Windsor Hum,” reported around Windsor, Ontario, beginning near 2011 and suspected — though never conclusively proven — to originate from heavy industry across the river in Detroit), as well as in Australia, New Zealand, South Africa, and cities across continental Europe.

2012 — The World Hum Map is born. A Canadian high school teacher and university lecturer named Glen MacPherson began hearing an unexplained hum after moving to a community on the west coast of British Columbia. When he relocated to a nearby town, the sound vanished. Unsatisfied with the conspiracy-heavy discussions he found online, MacPherson built a more disciplined space for tracking reports: the World Hum Map and Database Project. Over the following decade, the project grew to include thousands of geotagged, vetted reports from self-identified hearers around the world, and MacPherson became one of the phenomenon’s most visible independent researchers, giving interviews to outlets including the CBC, Al Jazeera, and Global News.

Recent years — Oslo, Norway. According to Norway’s public broadcaster NRK, residents around Oslo have also reported an unexplained humming noise a couple of years ago, underlining that this is not a phenomenon confined to any one country or decade.

2026 — The NTNU study. Drexl and colleagues Bonifaz Baumann, Andrej Voss, and Carlos Jurado publish their findings — titled “On the potential sources of a low-frequency sound percept that only a few can perceive” — in PLOS One, after testing 28 self-identified hum-hearers in Germany.

Who Are the Key People?

Markus Drexl is a professor at NTNU and the lead investigator behind the new study. His interest in The Hum grew out of a broader research focus on low-frequency sound and how the human ear processes it — an area he describes as understudied compared to the higher frequencies used in speech and music. Working alongside two PhD research fellows and a postdoctoral researcher, Drexl set out to test two competing, testable explanations for the sound rather than simply cataloguing more reports.

The 28 study participants were residents of Germany who had self-identified as hearing an unexplained hum or buzzing sound. They form one of the more rigorously tested groups of hum-hearers examined to date, though the researchers themselves caution that a sample of this size cannot settle the question for every hum-hearer worldwide.

Glen MacPherson, while not part of the NTNU research team, remains one of the most prominent independent figures associated with The Hum. A former University of British Columbia lecturer and high school teacher, he has spent more than a decade collecting self-reported data through the World Hum Map and Database Project, giving the phenomenon a level of organized, long-term documentation it lacked in earlier decades.

Joe Mullins, the University of New Mexico engineering professor who led the 1993 Taos investigation, represents the earlier, environment-first generation of hum research — one focused on finding an external physical source rather than examining the biology of the listener.

The Bigger Context: Why Nobody Could Find the Source

For most of The Hum’s history, investigations followed the same basic logic: something out there must be making this noise, so go find it. That approach makes sense — plenty of low-frequency noise really is generated by human activity and by nature alike. Many technologies can generate low-frequency noise, including ventilation systems, heat pumps, road traffic and windmills. Nature also produces sounds in this range through sources such as ocean waves striking the shore and wind moving across the landscape.

The trouble is that low-frequency sound is notoriously difficult to trace. Its long wavelengths let it travel much farther than higher-pitched noise, and the human ear is comparatively bad at judging which direction a low rumble is coming from. That combination has been enough, on its own, to send investigation after investigation down dead ends — even when a real external sound source genuinely existed somewhere in the vicinity.

At the same time, a very different explanation was circulating on the fringes: that The Hum wasn’t a sound at all in the traditional sense, but something manufactured, from secret military testing to microwave weapons to extraterrestrial activity. Serious researchers, including MacPherson, have deliberately kept this kind of speculation out of their work, insisting on physically testable explanations instead.

The NTNU team’s contribution was to formalize a middle path that had been floated for years but rarely tested directly: that the explanation might not be “out there” or “made up,” but rather a real, physiological event happening inside some hearers’ own auditory systems.

What the Researchers Found

Drexl’s team tested two specific, falsifiable hypotheses.

Hypothesis one: exceptional hearing. Perhaps hum-hearers simply have unusually sharp hearing in the low-frequency range, letting them pick up faint external sounds that are genuinely there but too quiet for everyone else. To test this, the team measured participants’ hearing thresholds at low frequencies.

The result: most showed no exceptional ability in this range. Only two people had better than average hearing at certain low frequencies. As Drexl put it, “Even though the group we tested was small, it still means that the hypothesis of having especially good hearing for low-frequency sounds does not hold for most people.” He did flag one caveat worth remembering: standard hearing tests may be too coarse to catch extremely narrow bands of unusually sharp hearing — the kind of gap that might only show up between, say, 50 and 51 hertz.

Hypothesis two: the ear itself as the noisemaker. The inner ear’s cochlea naturally produces faint sounds of its own, a normal by-product of how it amplifies incoming noise — typically in a range roughly between about 500 and 5000 Hertz. These are called oto-acoustic emissions, and in rare cases they can be picked up by a sensitive microphone placed in the ear canal — and even consciously perceived by the person producing them, sometimes as tinnitus. The team tested whether their hum-hearers were picking up their own low-frequency oto-acoustic emissions.

Here again, the answer was no.

What was left standing: low-frequency tinnitus. Having ruled out both an unusually sharp external-hearing explanation and a measurable internal-emission explanation for most of the group, Drexl’s team arrived at a third possibility — one that can’t be measured directly with current tools, but fits the pattern better than the alternatives. “Then there are people who hear something that cannot be measured objectively. We believe people in this category have a form of low-frequency tinnitus,” Drexl said.

Tinnitus is usually associated with a high-pitched ringing, but it doesn’t have to be. It occurs whenever the brain perceives a sound that has no outside source — and crucially, sufferers very often assume, at least at first, that the sound is coming from somewhere in their environment. It’s only when the noise persists after they leave the house, the neighborhood, or even the country that some hum-hearers begin to suspect the source is traveling with them rather than waiting for them somewhere outside.

Drexl’s overall conclusion draws a careful, two-part picture rather than a single tidy answer: a small number of genuine hum-hearers may indeed have unusually sensitive low-frequency hearing that lets them detect real external sound the rest of us miss. But for most of the people in his study, the likelier explanation is a form of subjective tinnitus that begins inside the auditory system itself, even though it feels completely external.

Questions That Remain Unanswered

The NTNU study is a meaningful step, but it is not a final verdict, and Drexl is careful not to present it as one.

Why does the illusion feel so convincingly external? Tinnitus explains a perceived sound with no outside cause, but it doesn’t fully explain why so many hearers are certain, often for years, that the noise is coming from a specific direction outside their home.
Could ultra-precise hearing gaps still be hiding real external cases? Drexl himself notes that standard audiometry may not be fine-grained enough to detect extremely narrow bands of unusual sensitivity, meaning a subset of “no exceptional hearing” results could be misleading.
Why do documented external low-frequency sources — like the industrial noise partly linked to Kokomo, or the suspected Zug Island sources near Windsor — coexist with cases like Taos, where extensive monitoring turned up nothing? The current research doesn’t unify these different patterns into one single mechanism, and the study’s authors don’t claim it does.
What explains geographic and demographic patterns in hum reports — for instance, why they cluster more heavily in certain regions and reportedly skew toward middle-aged hearers, according to independent data gathered by the World Hum Map project? Neither this study nor prior ones offer a settled explanation.
A note on scale: with only 28 participants from a single country, the study itself cannot confirm how widely its findings apply to hum-hearers elsewhere in the world.

These are gaps the researchers acknowledge, not weaknesses hidden from view — a distinction worth holding onto given how much speculation has surrounded this topic for fifty years.

Public Reaction

The Hum has always attracted an unusually wide range of reactions, and this study is unlikely to change that pattern overnight. Longtime hearers and hum communities — including contributors to MacPherson’s World Hum Map — have spent over a decade explicitly resisting purely psychological or “it’s all in your head” explanations, in part because tinnitus can carry a stigma of being dismissed as imaginary or exaggerated. For many sufferers, a diagnosis rooted in the auditory system rather than a hidden machine somewhere in the neighborhood may feel like both vindication (it’s a real, physiological phenomenon) and a letdown (there may be no factory to shut down, no fix waiting at the source).

At the same time, journalists and skeptics who have covered The Hum’s decades of dead-end investigations — from the inconclusive Taos study to the unproven Windsor “Zug Island” theory — have generally welcomed research that offers a testable, biologically grounded mechanism rather than another unconfirmed environmental suspect.

What Happens Next?

Drexl frames this study less as a final word and more as an invitation for further research. His broader argument is that hearing science as a field still doesn’t understand low-frequency sound and infrasound nearly as well as it understands the frequencies used in speech and music — a gap he says needs to close before regulators, engineers, and doctors can properly evaluate complaints about modern low-frequency noise sources like heat pumps, wind turbines, and traffic.

Practically, that likely means:

Larger, multi-country studies testing the same two hypotheses — exceptional low-frequency hearing and audible oto-acoustic emissions — in bigger and more diverse groups of hum-hearers.
Finer-grained hearing tests capable of detecting the kind of narrow-band sensitivity that standard audiometry might currently miss.
Continued independent data collection through projects like the World Hum Map, which can help researchers spot patterns — geographic, seasonal, or demographic — that a single lab study can’t capture on its own.
Parallel work on regulating and understanding genuine external low-frequency noise sources, since Drexl’s findings don’t rule out real environmental cases entirely, only show they don’t explain most of his study’s participants.

Conclusion

The Hum has spent fifty years resisting explanation, partly because the people investigating it kept asking only half the right question. They searched buildings, power lines, and mountainsides for a hidden machine, when for many hearers the “machine” may have been running quietly inside their own ears the entire time.

Markus Drexl and his colleagues haven’t closed the case. Real external hums, like the industrial hints found near Kokomo or the still-unproven suspicions surrounding Windsor’s Zug Island, remain part of the picture, and some individuals may simply hear better than the rest of us at frequencies most tests don’t even check. But their work reframes a fifty-year mystery in a way that finally fits the evidence: not as one single hidden sound waiting to be found, but as several different phenomena that have been mistaken for the same thing — some environmental, and for many hearers, one deeply, quietly human.

For the millions of people worldwide who’ve spent sleepless nights straining to place a sound no one else can hear, that reframing may be the most useful thing science has offered them in half a century: not a machine to switch off, but a reason to finally stop searching outside their own front door.

Sources: ScienceDaily / Norwegian University of Science and Technology (NTNU); Baumann, Voss, Jurado & Drexl, “On the potential sources of a low-frequency sound percept that only a few can perceive,” PLOS One (2026); Norwegian Broadcasting Corporation (NRK); the World Hum Map and Database Project (thehum.info); and historical reporting on the Bristol, Taos, Kokomo, and Windsor hum cases.