The complaints began, fittingly enough, very quietly. In the early 1990s residents of Taos, New Mexico — a high-desert town better known for adobe architecture and artists' colonies — began reporting a maddening low rumble, like a diesel engine idling a few streets away that never drove off. It was worse at night, worse indoors, and earplugs did nothing, which is not how sound is supposed to behave. Sufferers described lost sleep, headaches and a constant pressure in the ears. The story went national, and in 1993, after residents petitioned Congress, a team of investigators drawn from the University of New Mexico, Sandia National Laboratories and other institutions arrived with sensitive acoustic and electromagnetic instruments. A survey of some 8,000 households found that roughly two per cent of respondents heard the sound. The instruments heard nothing at all: no acoustic signal and no electromagnetic anomaly matching what the self-described "hearers" reported. The Taos Hum entered folklore as the noise that officially is not there.
Taos supplied the famous name, but Britain got there first. In 1977 the Sunday Mirror asked its readers "Have you heard the Hum?" and received hundreds of replies. Bristol became the classic British case: through the 1970s residents complained of a low, pulsing drone that was variously blamed on factory ventilation, gas mains and motorway traffic, and never conclusively pinned on any of them. Largs, on the Firth of Clyde, has hosted a well-documented hum since the 1980s. Comparable reports have come from Auckland, Bondi and dozens of other places. Wherever it appears the pattern repeats: a small minority hear it clearly, most people hear nothing whatever, and the microphones tend to side with the majority.
The hum with a return address
Occasionally, though, the microphones win one. From around 2011 residents of Windsor, Ontario, directly across the river from Detroit, complained of a rumble strong enough, they said, to rattle windows and shake beds. The Canadian government funded an investigation, and in 2013 researchers from the University of Windsor and Western University reported that the likeliest source was Zug Island, a heavily industrialised islet on the Michigan side crowded with blast furnaces. The American operators declined to cooperate with monitoring, so the case was never formally closed — but when steelmaking on Zug Island was idled in 2020, the complaints largely faded with it. The Windsor Hum is the rare specimen with a plausible return address.
Kokomo, Indiana, offers a messier lesson. After residents complained of a hum in the early 2000s, the city commissioned an acoustic survey that identified two industrial culprits — a cooling-tower fan and an air compressor. Both were duly quietened. Some residents reported blessed relief; others insisted the hum continued exactly as before. The external source, it seemed, had only ever been part of the story.
Inside the ear, or out in the world?
Across surveys the figure of roughly two per cent of people recurs, and the typical hearer is middle-aged. Descriptions are strikingly consistent: a low throb somewhere around the 30-to-80-hertz range, like an idling lorry engine, strongest indoors and at night, when masking background noise falls away. Strangest of all, some sufferers report that the Hum travels with them — still audible on holiday, hundreds of miles from home, which no factory fan can explain.
Explanations divide into two camps. Genuine low-frequency noise — from industry, traffic, pumps and pipelines — is real, carries over enormous distances, penetrates walls easily and is notoriously difficult to localise, so some hums are surely ordinary acoustics still waiting for their culprit. But Geoff Leventhall, the British acoustician who is perhaps the world's leading authority on low-frequency noise, concluded that many cases are probably generated within the auditory system itself — a percept akin to tinnitus, pitched far lower than the familiar ringing. On this reading the Hum is not imaginary, and not a hallucination in any dismissive sense; it is a real perception without an external source, which is precisely why the instruments draw a blank. Since 2012 Glen MacPherson, a Canadian teacher and researcher, has run the World Hum Map, an online database logging thousands of hearer reports worldwide in search of a pattern.
And sometimes the truth is stranger than either camp allows. In the 1980s houseboat residents of Sausalito, California, were tormented on summer nights by a droning that was eventually attributed to the plainfin midshipman, a toadfish whose males genuinely hum — a sustained drone produced by vibrating the swim bladder — to attract mates. Every hum, in other words, deserves its own investigation. But the unsettling residue of all the unsolved ones is this: a sound can be entirely real to the person who hears it and invisible to every instrument we own — and for roughly two people in every hundred, silence has never been silent.
Quiz nuggets
- The 1993 Taos Hum investigation surveyed some 8,000 households and found roughly two per cent reported hearing it, while instruments detected nothing.
- In 1977 the Sunday Mirror asked readers "Have you heard the Hum?" and received hundreds of replies; Bristol became Britain's classic case.
- A 2013 Canadian study traced the Windsor Hum to Zug Island's blast furnaces, and complaints faded when steelmaking there was idled in 2020.
- Sausalito's 1980s houseboat hum was attributed to the plainfin midshipman, a toadfish that hums to attract mates.
- The World Hum Map, logging hearer reports worldwide, was started in 2012 by Canadian researcher Glen MacPherson.