Imagine a low drone, like a distant idling engine or a refrigerator humming through a wall, except there is no engine and no refrigerator, and it never stops. Now imagine that you can hear it and the person sitting next to you cannot, and that when you ask anyone else about it, they look at you as though you’ve lost your mind. For a small number of people in and around Taos, New Mexico, this has been their everyday reality for more than thirty years, and a full government investigation eventually ended with a word nobody wanted: mystery.
The Taos Hum is one of the most studied unexplained sounds on Earth, and what makes it fascinating isn’t a ghost or a conspiracy. It’s a simple, stubborn contradiction. People hear it clearly enough to match its pitch. The instruments built to detect it found nothing at all, and the local background noise was quieter than the human ear can register… It’s the kind of puzzle that keeps me up at night, which is ironic given it’s a sound that keeps people up at night.
What Is the Taos Hum?
The Taos Hum is a persistent, low-frequency droning noise reported by a small minority of residents around Taos, New Mexico, since at least the early 1990s, that no instrument has ever been able to record. Those who hear it describe a low, steady hum, often worse at night, sometimes pulsing. It’s typically heard indoors as much as outdoors, and it seems to follow the listener around rather than coming from any fixed direction. The phenomenon isn’t unique to Taos, but Taos is where it drew the most attention, and where the most serious investigation took place.
The reports go back further than most people assume. A 1973 report in New Scientist described a university study of fifty people complaining of a “low throbbing background noise” that others couldn’t hear, always peaking between 30 and 40 hertz, usually heard in cool weather with a light breeze, often in the early morning, and usually confined to a zone about ten kilometers wide. A similar British study was reported in 1979. So the phenomenon the world calls the Taos Hum has quieter cousins stretching back decades before Taos became famous for it.
Why Did the Government Investigate?
Because residents got the attention of New Mexico’s congressional delegation, and the resulting 1993 study was deliberately public and open from the start. That openness wasn’t accidental. Many residents suspected the government itself was the cause, imagining secret facilities or military transmitters, and the investigators wanted to be seen to have nothing to hide. The team was led by Joe Mullins, a mechanical engineering professor at the University of New Mexico, and included researchers from Los Alamos National Laboratory, Sandia National Laboratories, and the Air Force Phillips Laboratory, about a dozen investigators in total, with hearing scientist James Kelly joining later to handle the auditory side.
They did what you’d want them to do, and then some. They surveyed eight thousand residents in Taos and the surrounding towns and got 1,400 replies. They ran acoustic, seismic, magnetic and electromagnetic measurements. They tested ten self-described hearers with a matching experiment, playing tones and asking the hearers to tune them until they matched what they heard. They built a custom low-frequency microphone, an eighteen-inch woofer sensitive enough to pick up very faint sound from 8 to 80 hertz, and nicknamed it the big ear.
Who Hears It, and What Does It Sound Like?
About two per cent of the population are hearers, and the pitch they report falls mostly between 32 and 80 hertz. The two per cent figure is a lower-bound estimate, drawn from 161 self-identified hearers out of 8,000 surveys, so the true proportion could be higher. Most of those who hear it are between 30 and 59 years old, and men and women are roughly equally represented. Sixty-two per cent of hearers perceive it between eight at night and nine in the morning, which fits the common report that it’s worst in the quiet hours. Some reported hearing it more than fifty miles from Taos.
In the matching tests, eight of the ten hearers could reliably tune a played tone to match their hum. Musicians among them placed it near E-flat, around 41 hertz. Technically-minded hearers described it as amplitude-modulated, a carrier tone running somewhere between 30 and 80 hertz with a slow pulsing modulation of 0.5 to 2 hertz, which is what gives the hum its throbbing quality. Whatever this is, the people hearing it aren’t making it up or misremembering. They consistently and reproducibly identify a very specific frequency.
What Did the Measurements Find?
Nothing. The acoustic, seismic, magnetic and electromagnetic sweeps all came back with nothing that could explain the hum. This is where the mystery really begins. The acoustic measurements found no signal that could account for it. The seismic readings recorded only background noise, and one dramatic event turned out to be a gopher digging its burrow past the geophone. The magnetic readings found only ordinary natural phenomena, and the electromagnetic sweep, from 20 hertz to 18 gigahertz, found nothing that wasn’t explained by power lines, radio and television, or lightning.
Then came the finding that raised the stakes. Some residents suspected a Navy transmitter, so the team looked at the relevant frequency range and found nothing above background noise. But the strangest result was simpler and more unsettling: the hearers could still perceive the hum even when the matching signal was switched off, and the local background noise was sitting 15 to 20 decibels below the threshold at which humans can hear anything at all in that band. You can usually only perceive beats, the slow pulsing interference between two sounds, if there are two genuinely separate tones present. The hearers reported beats. No microphone ever found the second tone.
What Are the Possible Explanations?
Researchers have floated several ideas, from tinnitus to the ears making their own faint sounds, but none is settled. The team considered low-frequency tinnitus, but were skeptical, because tinnitus is usually matched at much higher frequencies, three to six kilohertz, and rarely below one. They found that hearers reported beat-like effects that aren’t typical of tinnitus. Spontaneous otoacoustic emissions, the faint sounds the inner ear itself can produce, were seen as a plausible candidate; between 38 and 60 per cent of adults with normal hearing produce them, though most are unaware. Other proposals, from jet-stream shearing against the ground to high-pressure gas pipelines to military aircraft, have been suggested and disputed over the years, and none has been confirmed for Taos.
The honest way to understand the family of hums around the world is that some really are machines, and some are perception. The Windsor Hum in Ontario was traced, at least partly, to an American industrial site across the water, and stopped when blast furnaces there were shut down. The Kokomo Hum in Indiana was traced to a cooling tower and an air compressor. The Sausalito Hum in California turned out to be the mating call of male midshipman fish, resonating through the hulls of houseboats. Those cases were solved. Taos, and a handful of others like the long-running Bristol Hum in England, never were, and remain in the “we don’t know” column, which is precisely why they fascinate us.
The audiology expert David Baguley suggested that roughly a third of hum cases are grounded in a real physical source, while about two thirds come from people focusing too intently on innocuous background sound. Even so, he added that the majority of individual cases still end up unexplained.
So What Is the Taos Hum, Really?
The most defensible answer is that it may not be one thing at all, but a family of phenomena wearing a single name. Some hums turn out to be industry or machinery or even fish. Some appear to be generated, at least in part, inside the listener’s own ears or brain. Taos, with its negative results and its reproducible pitch matches and its impossible beats, sits uncomfortably between the two, and the 1995 report said it plainly: “we are left with a mystery.”
What I love about this one is that the investigation quietly changed shape. It started as a hunt for a source, an industrial plant or a secret transmitter, and it ended as a study of the human ear. The microphone could not hear what dozens of people could, and the background noise was below the floor of hearing, which means either a handful of people have extraordinarily acute low-frequency hearing, or the sound is partly made inside them. That’s a much stranger and more interesting outcome than any conspiracy… There are plenty of other unexplained phenomena that turn out to be examples of the same thing, people noticing something real that the instruments can’t reach. If you’ve ever heard a hum no one else could, you’re in rarer company than you might think.
