Bathroom fan making low frequency humming noise

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  #1  
Old 12-04-20, 08:52 AM
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Bathroom fan making low frequency humming noise

I recently started to hear a consistent low frequency humming noise in my bedroom (2b2b). Using one app, I identified it to peak at 120 hz but the decibel is below noise level. Yet I can hear it at night and cannot sleep. The electricians of my apartment complex do not believe in me, since a decibel detector does not show a noise level sound. However, I do noticed one time the sound started and stopped, so I believe it is not my illusion.

I decided to find out by myself. By shutting power off one by one on the electric panel, I found the source as the bathroom fan circuit. I am not an expert, so I can only give the following interesting observation:

1. The sound peaks at 120hz and 60hz.
2. It peaks at certain points other than the bathroom, one point in my bedroom, and one point in front my bedroom door, and another point in front of my second bedroom.
3. It is gone only when I turn off both fans of bathroom 1 and 2.
4. If either fan of bathroom 1 or 2 is turned on, then I can hear the sound at all the points in (2) above.

Does anyone know what probably is going on?
 
  #2  
Old 12-04-20, 10:04 AM
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That's simple, you are hearing the fan running. The sound vibration is probably being transmitted through the framing of your apartment. If you pay attention you can also probably hear other people's tv's, washing machine...
 
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Old 12-04-20, 11:24 AM
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Thank you. I have been living here for 3 years and just notice that sound. I believe that sound is in the background of the fan running sound. And combining with the fact that when bathroom 2's fan is on, I can hear the sound on the other side in the bedroom 1, I am a little concerned.
Again, I am not an expert. (I pretty much know nothing about this.) Do you know whether there is a electric part of the ventilation system that can affect each other between the two bathrooms and can make a electric humming? The layout is attached. layout
 
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Old 12-04-20, 12:27 PM
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You're hearing a "beat tone" aka "constructive interference" because one fan is running at a slightly different speed.


Try removing the grating and cleaning the accumulated lint off of both fan blades so they run at the same speed. I'd also check that they both spin easily, could be a worn or dry bearing causing a slight drop in the RPM of one fan.

 
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Old 12-04-20, 03:00 PM
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I was just going to comment about flying a twin engine propeller airplane and getting the prop rpm's out of sync. It creates an eerie waaawww waaawww... sound. Some may have heard it when flying in a propeller commuter airliner.
 
  #6  
Old 12-04-20, 03:24 PM
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It's quite possible that sound is a low frequency hum, but the cell phone is picking up the harmonics at 60hz and 120hz.

Does it sound something like these?
The Superheterodyne Radio: - https://youtu.be/hz_mMLhUinw?t=111

 

Last edited by Hal_S; 12-04-20 at 04:07 PM.
  #7  
Old 12-04-20, 06:43 PM
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This is very possible, your idea enlightened me!
 
 

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