I recently completed a bathroom remodeling project. During the course of the project, I started to notice a thumping noise coming from the drains (and/or toilet). The thumping sound sounds like the opening to Law & Order (https://youtu.be/gP3MuUTmXNk?si=uGn7OwV-zY70cm_d). It always occurs in pairs (2 thumps). I presumed, during the course of the project, that this may be related to the traps being dry...but now that the project is done and the traps have water, the thumps are still happening.

It does not seem to occur with use of the plumbing (like running the faucets, flushing toilet, etc). It is not a Knocking sound like would be typical of a pipe banging against the studs or an in balance of water pressure. It also does not appear to be related to temperature differences in the pipes as it occurs at all times of day.

I know it sounds crazy, but the thumps seem to occur whenever someone drives past the house (and perhaps over the manhole cover on the road immediately in front of my house). I realize that the storm sewer is not connected to the waste water lines, but that is the only consistent cause/effect that I can surmise.

Any thoughts on why this is happening or how to troubleshoot it? It's only been a week since we finished the project and it's already driving my family crazy.

My plumber has no idea what is causing it.

Thanks in advance for your input.

  • First thing would be to go stand out in the street & wait for a car to run over the manhole cover.
    – Tetsujin
    Commented Oct 26, 2023 at 16:28
  • I can see the manhole from my home office...and hear the cars go by. That is how I came up with the correlation
    – user176271
    Commented Oct 26, 2023 at 16:35
  • I think Tetsujin wants to know if the cover wobbles/moves when being driven over, or even walked on. The timing seems to match, but would need to time your trumps timing to front/back wheels driven over the cover to see if they match. Weird.
    – crip659
    Commented Oct 26, 2023 at 16:50
  • I thought he was trying to get me hit by a car :-) The manhole cover does not move when stepped on. But it does make noise when run over by a car....you can hear it wobble a bit.
    – user176271
    Commented Oct 26, 2023 at 18:22
  • Temporary test, put a construction cone on the lid so people would avoid it
    – Traveler
    Commented Oct 26, 2023 at 18:45

1 Answer 1


The idea of traffic causing noises in the sewer system is not far-fetched at all. Sound will travel through a sewer pipe for quite some distance. Have you verified the manhole outside the house is for storm sewer? (The lid should indicate.) The sanitary sewer will also have manhole covers and there's surely one or more of these near enough that sounds could carry to your house.

It might be that work was performed recently which prompted the removal of a manhole cover. A small stone or other debris may have gotten between the lid and its flange, so that a lid that fit well previously now wobbles and makes noise.

Perhaps you can work with an assistant so that one of you remains in the house listening for noises while the other drives a vehicle down the road, aiming for manhole covers. With a real-time connection by phone or radio you might determine which manhole cover, if any of them, contributes to the noises heard in the house. Of course this will be most effective if it's possible for you to do during a period of light traffic so that there are no other cars also hitting manhole covers during your test.

  • Greg. Thanks for your comments. I had a similar thought relative to troubleshooting. Waiting for my wife to get home to run the test that you suggest. Will also check the lid to see if it's storm or sanitary.
    – user176271
    Commented Oct 26, 2023 at 21:07
  • Confirmed that it is a Sanitary Sewer Cover...and Confirmed that when a car drives over it, it makes the thumping sound. Thanks so much for your insight. As a remedy, I presume that if the Manhole cover is reset, with no pebbles, debris that will fix it, right?
    – user176271
    Commented Oct 26, 2023 at 21:53
  • 1
    @user176271 Well I can't say for sure, but.. maybe resetting the cover will help! In my area those lids are about 20 inches diameter and cast iron or steel; very heavy and dangerous for unwary fingers that get into the wrong place. Perhaps if you call the sewer operator and explain they'd send somebody to clean out the lid/seat area for you.
    – Greg Hill
    Commented Oct 26, 2023 at 22:29
  • Glad that worked out for you. It was my first thought, to eliminate or confirm it was the same noise, transmitted via pipe or ground. Wish you luck getting the company to re-seat it for you.
    – Tetsujin
    Commented Oct 27, 2023 at 9:36
  • Thanks to everyone for your help.
    – user176271
    Commented Oct 27, 2023 at 11:51

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