The Hum is a generic name for a series of phenomena involving a persistent and invasive low-frequency humming noise not audible to all people. Hums have been reported in various geographical locations. In some cases a source has been located. A Hum on the Big Island of Hawaii, typically related to volcanic action, is heard in locations dozens of miles apart. The local Hawaiians also say the Hum is most often heard by men. The Hum is most often described as sounding somewhat like a distant idling diesel engine. Typically the Hum is difficult to detect with microphones, and its source and nature are hard to localize.

The Hum is sometimes prefixed with the name of a locality where the problem has been particularly publicized: e.g., the “Bristol Hum”, the “Taos Hum” or the “Bondi Hum”.

The essential element that defines the Hum is what is perceived as a persistent low-frequency sound, often described as being comparable to that of a distant diesel engine idling, or to some similar low-pitched sound for which obvious sources (e.g., household appliances, traffic noise, etc.) have been ruled out.

Other elements seem to be significantly associated with the Hum, being reported by an important proportion of hearers, but not by all of them. Many people hear the Hum only, or much more, inside buildings as compared with outdoors. Many also perceive vibrations that can be felt through the body. Earplugs are reported as not decreasing the Hum. The Hum is often perceived more intensely during the night.

In the Unsolved Mysteries segment called ‘Mystery Hum’, a tape re-creation of the Taos Hum was used for this segment. Robert Stack reported that one of the “Hum sufferers” created the audio tape, mainly for the purpose in that particular segment. This was done since their audio equipment didn’t pick up low-frequency sounds very well, and so that the show’s viewers and other non-“Hum sufferers” would get an idea of what the actual auditory phenomenon sounded like.

On 15 November 2006 Dr. Tom Moir, of the University of Massey in Auckland, New Zealand, made a recording of the Auckland Hum and has published it on the university’s website. The captured hum’s power spectral density peaks at a frequency of 56 hertz. In 2009, the head of audiology at Addenbrooke’s Hospital in Cambridge, Dr. David Baguley said that he believed people’s problems with hum were based on the physical world about one-third of the time and the other two-thirds stemmed from people focusing too keenly on innocuous background sounds.

It was during the 1990s that the Hum phenomenon began to be reported in North America and to be known to the American public, when a study by the University of New Mexico and the complaints from many citizens living near the town of Taos, New Mexico, caught the attention of the media. However, in the 1970s and 1980s, a similar phenomenon had been the object of complaints from citizens, of media reports and of studies. It is difficult to tell if the Hum reported in those earlier cases and the Hum that began to be increasingly reported in North America in the 1990s should be considered identical or of different natures. During the last decade, the Hum phenomenon has been reported in many other cities and regions in North America and Europe and in some other regions of the world.


Some explanations of hums for which no definitive source has been found have been put forth. These include:




Spontaneous otoacoustic emissions

Colliding ocean waves