I t was around 2005 that Simon Payne started hearing it. A strange, low, rumbling sound that travels through walls and floors and seems to come from everywhere. At first, he was convinced the noise was from some kind of machinery, but he couldn’t find the source.

It didn’t go away; he couldn’t run from it. Even when he travelled 12,000 miles from his Cambridgeshire home to New Zealand, he could still hear it. It wreaked such havoc on his life, he had to quit his job.

He became increasingly isolated and stopped seeing friends. But when he started to look around on the internet for more information, he discovered he was not alone. “I found out that it was all over the place,” he says.

“There’s no hiding from it.” Payne was hearing “the Hum”, a mysterious global phenomenon that is thought to affect as many as 4 per cent of the world’s population. The earliest reliable reports of the Hum date from the Seventies , when numerous Bristol residents wrote letters to the Bristol Evening Post to complain about hearing the noise, which has since been compared to the sound of an idling truck or thunder – and is different from tinnitus .

Some Bristolians still hear it to this day, and it’s been reported in places around the world, from the suburbs of Tokyo to Taos in New Mexico and Largs in Scotland. It’s left many “hearers” anxious and depressed, and has been linked to several suicides. Over the years, many theories have been posed and investigations conduc.