Residents of Bristol are reporting the return of a mysterious hum which has been heard for more than three decades.
The "Bristol hum" made the news in the late 1970s, when residents complained to the council about a strange noise.
For the past fortnight, several Bristol residents have reported the low-pitched humming noise on social media.
In a YouTube video uploaded on 4 January, a man claims to have recorded a noise matching the description of the hum.
The noise has been blamed on various causes, such as low-frequency submarine communications, phone masts, wind farms and leaking gas pipes.
“For the first few years I lost sleep, couldn’t concentrate and was unable to do anything. I was constantly in tears, which put a great strain on my husband. It has changed me from an active, creative person to a stifled, angry pessimist,” a woman told The Independent in 1994.
Scientists now think the noise is caused by the pressure of waves vibrating on the ocean floor.
Researchers at Centre National de la Recherche Scientifique in France said the pressure of the waves on the seafloor generates seismic waves which cause the Earth to oscillate, producing the droning sound.
