In north-central New Mexico, the town of Taos has been home to many famous residents, including Julia Roberts, Dennis Hopper, D.H. Lawrence, Aldous Huxley, and Donald Rumsfeld. It's a small, laid-back, artsy community that is also home to an unusual mystery: a resident hum of unknown origin, the so-called "Taos Hum."

Various theories have been offered as an explanation, ranging from the mundane to the fantastic, the psychological to the paranormal. Stoned hippies, secret government mind control experiments, underground UFO bases, and everything have been blamed.

The hum seems to have first been reported in the early 1990s. Joe Mullins, a professor emeritus of engineering at the University of New Mexico, conducted research into the Taos Hum. Based on a survey of residents, about 2 percent of the general population was believed to be "hearers," who claimed to detect the hum. Sensitive equipment was set up in the homes of several of the "hearers," measuring sounds and vibrations, but after extensive testing, nothing unusual was detected.