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.