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All around you are sounds, right? You might be reading this on a laptop with a whirring fan, or on your phone on a rattling subway, or even at home, with music or the air-conditioner on, adding a thin layer of white noise to everything you hear.
Now take all that away. What's left?
For about 2% of people, it's "the hum."
Writing in this month's issue of The New Republic, reporter Colin Dickey tries to chase down "the hum," a mysterious sound (like "a low, distant rumbling") that has been haunting people for at least four decades - particularly those who live in quiet rural areas, where traffic and the upstairs neighbors aren't around to drown out the low thrumming they insist is there.
Dickey trawls Facebook and Reddit looking for theories behind the low noise that's been reported in locales as far apart as Tasmania to Reykjavik, trying to suss out whether the sound actually exists in the world - or only in the minds of those who hear it:
Dismissed by governments and mainstream researchers, Hum sufferers become demoralized, despondent. In such isolation the discourse festers, breeding conspiracy theories and kooks ... On a Facebook page for Hum sufferers, one rambling post describes how "advanced satellite technology" is being used as "a brutal torture instrument by transmitting sounds, voices, and images directly into the brain, creating numerous pains and sensations throughout the body and significantly altering energy level and emotional states."
Some of the posters go so far as to attribute bizarre criminal acts (like driving through a White House checkpoint) and mass shootings to people driven mad by the hum.
Dickey, after traveling to remote Gibsons, British Columbia, to meet with Glen MacPherson, creator of the World Hum Map and Database Project, ends up with more questions than answers.
But it turns out that hum-hearers might not be crazy: The Independent recently reported the results of a study that suggested the hum is more prevalent near certain geological features deep underwater and could be a result of "microseismic" activity along the sea floor.
It's possible that some people who hear "the hum" might be hearing the din of the ocean (or the wind or the trees). But they also might have tinnitus, a common symptom of many different ear and hearing problems.
The National Library of Medicine notes that while tinnitus is often thought of as a "ringing" in the ears, it can include a wide variety of low-level, persistent sounds, including - you guessed it - a hum.
But Dickey says that doesn't explain things. "The Hum," he writes, "defies a simple correlation with tinnitus."