A clamor needn’t be high-pitched to cause alarm. People in New Mexico, England, Canada, New Zealand, and elsewhere have reported hearing similar bouts of pervasive, low-frequency droning for decades. This tone has the added intrigue of not being audible to all. Some speculate that tinnitus, which causes ear ringing, could be a factor. But not everyone who claims to be one with the hum suffers from the condition. Could they be imagining a rumble based on others’ reports? If it actually exists, where does it come from? With such vague humming and hawing, it’s difficult to know where a serious inquiry would begin, so this sonic conundrum remains uncracked.