For the past couple of weeks there has been a periodic rhythmic mechanical humming occurring in my home that will go on and off for hours at a time. We're in a detached single family residence built in the 70s. According to a cheap oscilloscope app it's about 80Hz and repeats a little faster than 1 hum a second in a sort of "WUm-WUm-WUm-WUm-WUm" fashion. I don't have a measure of it's loudness but I can hear it over my ~20dB computer fans. We can only hear it indoors, even if we're outside right next to the house. It is louder in open rooms and near certain walls.
Things from other posts here that I've tried to rule out:
- Something mechanical outside -- At first we thought it was the wood chipper from a work crew taking down trees across the block from us. But they've been gone for a couple weeks now and it's still happening. Additionally, if I go outside and walk around the neighborhood to try and pinpoint the sound I stop hearing it the second I step outside my front door.
- Neighbor's AC condensers -- I've checked a couple times and they've been off at the houses to either side of us during the noise. Same with our condenser.
- Something electrical/hidden fan/pump/etc -- The noise continues even when I flip the main breaker.
- Overpressure in water pipes -- We'd had water hammer issues in the past and recently tested the pressure on our main line which measured 80psi. Finally, that must be the issue! Nope, had a new PRV installed a couple of days ago and the noise is still happening at 55-60psi. If anything, now it's louder.
I'm at a loss trying to figure out where this is coming from. Something plumbing-related is still my top guess but we tried clearing our pipes this morning and we could still hear it even with all the water drained from our home. I'm hoping someone here has advice on further steps I can take to troubleshoot this or an idea of who to talk to to get it fixed.