Scientists May Have Identified the Source of the Global Low-Frequency Hum Reported Since the 1970s

A variety of theories soon sprang up to explain the source of the unexplainable audio nuisance— according to the BBC, factory noise, electricity pylons, tinnitus, flying saucers (of course), and a secret government project were all put forth as possibilities.

In the early 1970s, the town of Bristol, U.K., was plagued by a low, persistent hum. It typically occurred at night, and it irritated local residents so much that they wrote letters to the local Bristol Evening Post to complain.

This humming phenomenon—which eventually became known simply as...