I'm having a bit of a mysterious problem. A couple of weeks ago I've replaced a dimmer switch in the upstairs bathroom. Of course while working on that I shut off the electricity for that part of the house. Since turning it back on we've been hearing this thumping sound which seems to be coming from the ceiling. The sound is extremely frequent: I've timed it and it's exactly every 2 minutes and 53 seconds.

At first I didn't link it to that dimmer job, because I thought it was water related (like water hammer). But after a couple of days of being annoyed with the sound I've decided to turn the electricity back off (same circuit breaker) and suddenly the sound stopped.

I did notice in the garage where the water comes in that the pressure was too high so I've already adjusted the pressure regulator lowering the pressure, but the problem persists.

I've also bled the water pipes using this info here: http://www.factsfacts.com/MyHomeRepair/PipeNoises.htm


Turn off the water to the house at the entry. Find the lowest faucet in your house--often this is an outdoor garden hose faucet--open this faucet and then open a few of the indoor faucets at high locations such as upstairs or at a wet bar and let the low faucet drain for 5 minutes or until it stops dripping, whichever takes longer. Close all the faucets and turn the main back on.

I suspect it has something to do with the fire sprinkler system. When I turn on the circuit breaker switch in the box I do hear water running, or so it seems. The only thing I can think of would be the sprinkler system.

Does anyone have an idea or pointer of what this could be? At this point I'm not even sure if I should call a plumber or an electrician.

Edit I've tried to record the sound with my phone, because it's hard to describe. Unfortunately the quality of the recording isn't great - the mic of the phone is unable to capture the full frequency spectrum. It sounds a lot louder and deeper in real life and I can actually feel some vibration in the floor when it happens. It sounds mostly like the sound of impact, what I would imagine a poltergeist to sound like. Here's the recording, you can hear the sound @ 0:18

Sound recording

Edit 2 As suggested by Tester101 here's a list of items on the circuit: - Two wallsockets in the master bathroom (not being used right now)

  • Possibly the control unit of the alarm system, but I'm unsure. It's inside of walk-in closet in the master bathroom.(1)

  • The light and fan in the downstairs bathroom

  • Light in the garage

  • The wall sockets in the living room, only some game consoles, a projector and a soundbar are connected to that

(1) The alarm system looks like it's not functional, but it does say something about smoke detection on the main unit so I'm thinking it might control the sprinkler system as well. We've only been living here since a year and we've never bothered to look at the alarm system since it looks dead.

  • I can't think that's water hammer. Can you send someone up into the attic above that bathroom to try & identify the source of the noise? It'd be a shame if it was a rat caught in the wiring, twitching occasionally. It might have something to do with a bathroom vent fan, though... Sep 22, 2015 at 23:01
  • @TDHofstetter Thanks for the feedback. I don't think it's water hammer anymore either, because after shutting off the main water valve the sound is still there. I'll try and check the attic to see if that gives any clues. I don't think it's rodents since the frequency of the sound is so extremely accurate. It's really every 2 minutes 50 something seconds. Also it can't be the bathroom vent, because that fan is controlled by a different circuit breaker. I'm still thinking it could have something to do with the fire sprinklers, because it sounds like a valve closing, sounds similar to the washer
    – Ruben
    Sep 22, 2015 at 23:17
  • Is your fire sprinkler system pressurized with an electric pump? This sounds like what you hear in an RV with a water system pressurized with an electric pump that will come on with a drop in pressure. Great question!
    – mikegreen
    Sep 23, 2015 at 5:50
  • @mikegreen Hmm that would actually make sense. The sprinkler system probably needs more pressure to be effective so it would need a pump for that. The only thing is that I would expect it to be located in the garage where the water comes in, but nothing like it. The sound does seem to come from one specific area of the house (hard to pinpoint exactly though), so that would match with that theory.
    – Ruben
    Sep 23, 2015 at 6:03
  • Coming out of left field here, but,.... I'm not sure what your space is like, but when I heard it, it reminded me of the sound that loose ducting makes when the central fan is turned on and off.
    – N8sBug
    Sep 23, 2015 at 10:20

1 Answer 1


I feel like an idiot but it turned out to be the subwoofer in the living room that apparently died while I was working on that dimmer. This is after checking the attic today, checking out the alarm system's control unit and lowering the water pressure last week. Since the sound seemed to come from the wall I just decided to unplug everything one by one and that's how I found out it's the subwoofer. Since it's against the wall the sound travels up and is amplified by the wall.

Yes I'm an idiot, but I'm glad it's solved at least. thanks for all the help and suggestions.

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