The earliest widespread reports of something resembling the Hum originated in England as early as the 1940s and 1950s, when pockets of concerned citizens across Britain started reporting a mysterious "humming, droning and buzzing sound" [source: Deming].
The "Bristol Hum" was the first outbreak to be linked to a specific city, in this case the southern English town of Bristol. In the late 1970s, a series of articles about the Hum in the U.K. newspaper the Sunday Mirror triggered a flood of mail from readers across Britain who had been suffering from the same maddening sound [source: Deming].
News of the Hum made enough noise — pun absolutely intended — to attract the first serious researchers. In a 1977 volume of the scientific journal Applied Accoustics, two researchers explored a "particular environmental noise phenomenon which appears to be a cause of real and severe disturbance to certain people" [source: Vasudevan and Gordon]. Their best guess was low-frequency sound waves generated by distant industrial sources.
Another famous hum began plaguing the residents of the coastal Scottish town of Largs in the late 1980s. It was the same low-pitched drone, inaudible to most, but debilitating to a sensitive few. The "Largs Hum," like other hums, is loudest indoors and at night, and can trigger nosebleeds, crippling headaches and chest pains in the worst cases [source: Barton].
In the U.S., the first large-scale outbreak of the Hum occurred in Taos, an artist's enclave in New Mexico. In the early 1990s, distressed Taos residents complained to their local and state representatives, eventually prompting an official Congressional investigation [source: Mullins and Kelly]. In 1994, Joe Mullins, mechanical engineering professor emeritus of the University of New Mexico, led a team of acoustic researchers and hearing scientists from nearby Los Alamos National Laboratory and Sandia National Laboratories to hunt down the source of the Hum [source: Mullins and Kelly].
Again, the research team's results were inconclusive — people were clearly suffering from the same tormenting sound, but investigators had no idea where it was coming from, and why it only affected 2 percent of the population [source: Mullins and Kelly].
A similar research effort was conducted in the sleepy Indiana town of Kokomo, where residents claimed that the Hum was so powerful it could make dead leaves "dance" on the ground and cause light bulbs to explode [source: Deming].
So who is more likely to be affected? In Britain, 75 percent of the Hum hearers were women, middle-aged and older, but in Taos, the hearers were almost evenly split between older men and women [source: Deming].
As to what is causing the Hum, there's no shortage of explanations.