Science & Health

The Mysterious Hum Heard Around the World May Finally Have an Explanation

An estimated 2 to 4 percent of people worldwide hear a persistent low-frequency hum that no one else can detect. After decades of speculation, researchers may have pinpointed what is really going on.

• The phenomenon known as "The Hum" was first widely reported in Bristol, England, in the 1970s, and has since been documented across the United States, Canada, Australia, New Zealand, and Europe.
• A team at the Norwegian University of Science and Technology tested 28 people who reported hearing the sound and found that neither external noise sources nor sounds produced inside the ear could explain most cases.
• The strongest remaining hypothesis is that many cases involve a form of low-frequency tinnitus — a phantom sound generated by the auditory system itself, even though it feels completely external.

The Hum typically manifests as a deep buzzing or droning noise, often compared to an idling diesel engine or a distant subwoofer. It is most noticeable indoors at night, when ambient noise is low and people are trying to sleep. Sufferers have described it as anything from a minor annoyance to a source of physical discomfort that makes rest nearly impossible.

The phenomenon first broke into public consciousness in the mid-1970s, when the Bristol Evening Post received a flood of letters from residents who could hear an unexplained sound. One early theory blamed industrial fans inside a department store warehouse, but the reports continued long after the warehouse closed. Similar accounts emerged from coastal towns across the United Kingdom, then from Taos, New Mexico, and Kokomo, Indiana, in the 1990s. The World Hum Map and Database Project, founded by Canadian teacher Glen MacPherson in 2012, has since collected reports from thousands of people worldwide.

Researchers at NTNU, led by Professor Markus Drexl, examined two main hypotheses. The first was that The Hum is an externally produced sound — perhaps from industrial equipment, traffic, ocean waves, or wind interacting with buildings. The second was that the ear itself might be generating the sound through spontaneous otoacoustic emissions, tiny vibrations produced by the inner ear. Neither explanation fit the majority of participants. The most consistent finding was that people who hear The Hum often have normal hearing but experience a phantom low-frequency perception — a specialized form of tinnitus that their brain interprets as coming from the outside world.

This distinction matters because it changes how the condition can be managed. If The Hum were an external noise, the solution would be acoustic shielding or engineering. If it is a form of tinnitus, cognitive behavioral therapy and sound therapy — approaches already used for conventional tinnitus — may offer relief. The researchers emphasize that the experience is real, not imagined: the brain is genuinely processing a sound signal, even if the source is internal rather than external.