Hum

About one person in twenty-five says they can hear a low hum, pulse, or rumble that nobody standing next to them can. It's been reported for decades, in enough places to get its own name — the Hum — and enough guesses at a cause (industrial machinery, buried pipes, secret transmitters) that most of them can't all be right. A March 2026 study (Baumann, Voss, Jurado & Drexl, PLOS ONE) took 28 people who hear it seriously enough to test them properly: room microphones, hearing thresholds, and a probe built to catch sound their own ears might be generating from the inside. It found no unusual hearing and no measurable emission from anyone's ear below about 900 Hz — hearers and controls alike. Their read: for many, probably not all, of these people, what they're describing is a rare, low-pitched form of tinnitus. A sound with no source outside the head at all.

Twenty-three of the 28 matched what they hear to a number, using an ordinary online tone generator adjustable in 1 Hz steps. Their median match was 50 Hz. Below is the same kind of tool, not a recreation of anyone's hum — drag to a frequency, listen, see if any of it means something.

Two honest gaps, not glossed over. First: most laptop and phone speakers roll off hard under about 60 Hz — the driver just can't move enough air down there — so headphones or a real speaker carry the low end of this slider more truthfully than a bare laptop will. Second, and bigger: this tone is a real sound wave, generated by your browser and pushed out through a speaker into the air and then your ear — an external stimulus, same as a car idling outside. What the study's own hearers describe, and what its own probe came up empty on, isn't that. If it's inner-ear in origin, as their own best guess holds for many cases, there is no vibration anywhere for a microphone — or this room — to ever catch. Playing a tone can't simulate a sound with no outside source. It can only hand you the same dial their own participants used to name one.

One more number from the same paper, unused above: only 39% of participants who hear it reliably at home could still hear it once they were sitting in the study's own lab. Whatever room, or silence, a hum needs to be heard in, this page can't reproduce that either.