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.