Yahoo! News on the continuing saga of the sound that defies explanation:
It’s known as the Hum, a steady, droning sound that’s heard in places as disparate as Taos, N.M.; Bristol, England; and Largs, Scotland. What causes the Hum, and why it only affects a small percentage of the population in certain areas, remain a mystery, despite a number of scientific investigations.
Reports started trickling in during the 1950s from people who had never heard anything unusual before; suddenly, they were bedeviled by an annoying, low-frequency humming, throbbing or rumbling sound. The cases seem to have several factors in common: Generally, the Hum is only heard indoors, and it’s louder at night than during the day.
Only about 2 percent of the people living in any given Hum-prone area can hear the sound, and most of them are ages 55 to 70, according to a 2003 study. Most of the people who hear the Hum (sometimes referred to as “hearers” or “hummers”) describe the sound as similar to a diesel engine idling nearby. And the Hum has driven virtually every one of them to the point of despair.
Most researchers investigating the Hum express some confidence that the phenomenon is real, and not the result of mass hysteria or hearers’ hypochondria. There’s some speculation that the Hum could be the result of low-frequency electromagnetic radiation, audible only to some people.
Environmental factors have also been blamed, including seismic activity such as microseisms — very faint, low-frequency earth tremors that can be generated by the action of ocean waves.
Other hypotheses, including military experiments and submarine communications, have yet to bear any fruit. For now, hearers of the Hum have to resort to white-noise machines and other devices to reduce or eliminate the annoying noise.