The Hum

     It is an affliction that affects thousands world-wide, and yet there is no explanation for it known to science -- medical or otherwise. To most of humanity, it doesn't exist. To those who hear it, it is known only as the Hum.

     It has been described as a persistent low-frequency humming, rumbling, or droning noise; some describe it as an 'idling engine' while others have described it as closer to an electrical array's steady drone. Vibrations have been reported to be felt throughout the body by some, although this may be psychosomatic in nature. Earplugs have not been reported to reduce the noise at all, which indicates to some that it's not an actual, physical sound -- but interestingly, those who have experienced it state that the sound lessens when moved away from, with a range measured in many miles.

     The phenomenon is not singular, but has been heard in many places, and those places that do have such occur generally call it by a localized name. The 'Laos Hum', the 'Bristol Hum', and similar names. A variety of explanations have been presented, none of which have ever been fully accepted, from tinnitus (unlikely to be so prevalent - up to 2% of the population of Laos, for instance - and similar in every case), to nocturnal fish sounds, to HAARP. The localization of these phenomena, however, suggest that there may be some unknown machine type that produces the 'Hum'.

     What do you think causes the Hum?