This dull, monotonous drone has been blamed for nosebleeds, sleepless nights and even a suicide.
It strikes apparently indiscriminately, having been reported in locations including Britain, Australia, New Mexico, and has now been recorded in Canada.
"The Hum" has it has become known, roused British Columbia resident Kimberly Wookey from her sleep on 29 August.
An appropriately creepy still from Kimberly Wookey's video, shot on 29 August
Wookey posted the footage on YouTube, explaining she had heard it once before on 19 June.
She wrote: "I was awoken by these sounds. I shot out of bed like a bat out of hell realising it was the same sounds I heard before and I ran around looking for a camera to try to capture them with."
Wookey recorded the sight - and sound using an HD Samsung SC-HMX20C Video Camera.
She added: "I have no idea what these sounds are but it is pretty strange."
Even stranger - only two per cent of people living in any given "Hum prone" area can hear the sound, with most of them aged 55 to 70, according to a 2003 study by acoustical consultant Geoff Leventhall, who has advised the British government on this issue.
Leventhall has never heard the hum himself and has only rarely been able to pick it up on recording equipment.
Katie Jacques told the same channel in 2009: "It's a kind of torture, sometimes you just want to scream."
Jacques, who had tinnitus ruled out, was 69 at the time, apparently confirming Leventhall's study.
The retired head teacher from Leeds added: "It has a rhythm to it - it goes up and down. It sounds almost like a diesel car idling in the distance and you want to go and ask somebody to switch the engine off - and you can't."
The BBC reports the Hum has been linked to at least one suicide, as well as headaches, sickness and nosebleeds.
Scientists have largely been baffled by the phenomena, though research indicates it is real and not some sort of mass hysteria, Live Science reveals.
Industrial equipment, high pressure gas lines, electrical power lines, wireless communication devices are among suspected sources, though the website adds that only in a few cases have they been directly linked to the Hum.
As for the latest manifestation of the Hum in Canada, city spokesman Alisa Thompson insists the noise was caused by a city worker grinding down the blade of a grader.
She told CBC News: "The grader blade needed to be straightened. Kind of gets ground down and it makes a very strange noise. It's as simple as that.
"The video, the YouTube video, is actually right around the corner from the arena, and that's where our employee was doing the straightening."
What do you think?