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I'm looking for ideas on what might cause the very deep hum I hear in my house when it's quiet. It's been present 24/7 for many years. When I'm alone in the house and nothing is turned on it's actually loud enough to be annoying, but it's not loud enough to record on my phone.

I live in a semi-rural residential neighborhood with no industry within miles. I can turn off my main breaker and the noise still present, so I assume it's not coming from inside my house. I'm 2 to 3 miles from an Interstate highway. Most of the time when I'm outside I cannot hear road noise from the highway. We have county water but no natural gas or sewer. It's slightly louder in my basement. It's not louder near where the water pipe enters the house.

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    Are you sure it's not in your head? Well, in your ears really. Tinnitus can be low frequency as well as the more common "ringing" sound. Try some noise cancelling headphones as a test. They will have no effect on tinnitus but will be quite effective against LF background noise.
    – jwh20
    Aug 16 '19 at 23:58
  • maybe there is a secret government research facility under your house ... look for trapdoors in your basement .... seriously, there may be a pipeline running underground .... or there may be a cave system near your house and you may be hearing wind noise from inside the caves
    – jsotola
    Aug 17 '19 at 0:28
  • @jwh20 The intensity changes as I move around the house. Also, I have high-frequency tinnitus, I can tell the difference. There are a lot of strange things running around in my head. This noise isn't one of them. :) Aug 17 '19 at 1:39
  • I was going to say utilities... But what would have made this story better is if you mentioned you have others that notice the exact same thing. Witness accounts account for A LOT. Incidentally, while replacing some plumbing lines in my crawl space beneath my home, I heard a strange hum too. I at first could not figure out where this him was coming from ... I then noted the open "out" main sewet line I had cut to make repairs.. Aug 17 '19 at 22:37
  • That's the source... sewer line ! Our sewage treatment plant is 9 miles away... Yes I could hear the plant / pumps running Aug 17 '19 at 22:48
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It could be the transformer for your house. Do you know where it is? On a pole? In a box on the ground? The noise should be distinctly louder as you get closer.

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A few possibilities come to mind.

  • Are there any high voltage power lines nearby, or other buried electrical on your property? Even though you turn off your main breaker, there might be some sort of induced electrical into your house.
  • Even though you're killing the main breaker in the house, is there an outside (or possibly buried) stepdown transformer from your electrical supplier that might be inducing the hum on your feeder lines to the house, or acoustically coming into the basement?
  • Does your main breaker control ALL electrical? Maybe a well pump or radon removal fan that's tapped off before the breaker you're throwing?
  • Any possible battery-powered mechanical fans/clocks/timers that might be making noise even with the power off?
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The intensity changes as I move around the house

Yes, this is normal.

Low frequency sounds create standing waves inside rooms. It's a bit like an organ pipe or a flute, where the acoustic wave bounces back and forth in a pipe. This creates resonances at certain frequencies whose wavelengths correspond to the length of the pipe. The same happens in a room where acoustic waves bounce between walls. Some frequencies will be amplified by this resonance.

Unfortunately, this depends on room dimensions, which you can't change. So if there is a source of noise in the environment that emits a frequency that corresponds to the resonance of your room, you have a problem.

I had this issue in a flat I used to live in, a constant low frequency hum that was very annoying. I traced it to a neighbor's ventilation fan that was clogged with dirt, so it was off balance and it vibrated. Cleaning it fixed the issue. Due to acoustic resonances the intensity of the hum would vary wildly depending on where I was in the building, so it was impossible to find it by ear. I had to stick a stethoscope on the walls to listen to the noise, and that helped locate the source.

You could record the hum with a good microphone to check if the frequency corresponds to mains, or a multiple of mains. But if you still have hum with the power cut off, then that may not be fruitful. If it is constant, then it is not the wind.

You can try opening and closing doors inside the house to see if that changes the hum sound. This changes the volume where standing waves can resonate. Also, the air inside a corridor can act like a mass/spring and resonate. So the solution may be just as simple as closing a door, or putting a curtain across the corridor that resonates.

If that doesn't work, and if you can't shut it down at the source, then you'll have to setup some bass traps.

First, try to measure the frequency of the hum. You can do that byear, or get/borrow a good microphone, record it with a computer, and use audacity's spectrum feature to get the frequency.

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Some possible items that can produce sounds are; transformers for a door bell or furnace, the ballast in a florescent light that is on, a computer and even some TV's. You could turn off the main circuit breaker for the house and if the sound goes away, then it is being produced by some electrical device. If it is an electrical item, then start by turning off each circuit breaker 1 at a time until you find the one that controls the sound.

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  • They mentioned in the question that they tried turning off the main breaker already. Aug 17 '19 at 22:26

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