So there's a weird humming noise in my apartment that pops out for a few hours a day and would keep me awake. I was hoping you guys might have heard of it and can tell me what the hell is causing this. My oscilloscope tells me it's 120Hz so I recreated this audio that my flatmate and I agree is pretty spot on:


This has been driving me crazy for months so thanks in advance for your help!

edit: I live in Boston, MA, and the AC is 60Hz if that's relevant at all

  • 6
    So this could be a fan in another unit with a worn motor or out of balance blade. Have you asked your neighbors above/below/around you if they are hearing this? – Jimmy Fix-it Dec 3 '19 at 4:05
  • We think it's our next door neighbor but they're not home so couldn't confirm. The people in one more door over say they don't hear anything tho. – littlesadcookie Dec 3 '19 at 5:48
  • sounds like a ceiling fan that is set on medium speed ... i have heard that sound from a number of fans – jsotola Dec 3 '19 at 8:36
  • Could also be a transformer mounted to the structure – Phil Freedenberg Dec 3 '19 at 15:24
  • Sounds like 120Hz added to 122Hz (or perhaps to 118Hz). – Daniel Griscom Dec 3 '19 at 17:08

I have found this a few times with incandescent lights and dimmers, most dimmers are SCR so they are turning on and off each cycle, the noise was actually coming from the element in the light, I did not quite believe it the first time I found this but figured it was because of the fancy shape of the chandelier lamps. A few years later I had it happen on some long life lamps the ones made to last 10 years with heavy filaments. And the last time was on a standard 60w clear lamp, all of these were on a dimmer and were quite noisy (I have poor hearing and could clearly hear them). So I would look at the lights as they may be the cause, change the level or turn off to see if it changes the noise.

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