Ok this is weird. For over a year I've been hearing only in the bathroom a sound that can best be described as a very soft muffled timpani drum, always two beats, always right in a row with maybe a quarter second between them (sorta that echoey sound the drum makes). I've heard it in one bathroom that is a full bath and one toilet closet (not sure if that is what it is called) it's in the master bath.

At first I thought it was coming from the vent fan ducts, but the other day I had the toilet pulled in the full bath and before I had stuffed a rag in the drain, that sound this time not muffled at all obviously came from the drain flange. I was kneeling near it.

Any ideas? Lived in the house for quite some time, have only heard the sound the last year or so. House built in 1998 and has plastic plumbing. It's relatively common, like 25% of the time I use the bathroom. I'm not the type to hang around the bathroom so not sure the time interval between sounds. It's prior to using any plumbing (flushes, sink, etc). I sometimes hear it when I'm walking by the bathroom and no one else is home.

I'll be going up to the roof soon to check on another issue and will take a look down the vent stack.

 

Sounds like its in the sewage pipes for sure. My guess is somewhere in the sewer system there is a water-air lock, and then it breaks. The sound from that travels up the sewer pipe. If you have your own septic tank I would pop the covers off and have a look. If its piped service from the municipality you could mention it to them. They might laugh or they might know that means something and go investigate.

 

Do you have a shower or floor drain that's rarely used? I've heard a similar sound from a first floor shower when the trap starts drying out. It's more of a gurgle than a drum, but maybe?

Dumping a half gallon of water down the trap every few weeks solves my problem.

 

Yes, but like you I have made sure there is water in the traps. Sound remains.

It is municipal. I'll ask them. Knowing that plastic pipe allow sound waves to travel far, who knows where this might be located. I can't think where it might be on my section of sewer line. What is unique is that the sound is exactly the same, boom boom in quick secession every time.

Going on what you said, it almost sounds like maybe a belly has developed somewhere that is just filling the pipe and makes that 'air break" every so often. I just didn't think it would be so identical each time.

I also thought it might be cars rolling over a manhole cover, but the sound is so quick. Also don't know the mechanics of what is below a manhole cover and how the sound might enter and travel.

Still haven't made it to the roof yet to check vent pipe. Maybe tomorrow.

 

Gee, that just might be it somehow. Sounds far fetched but I could buy that. A vehicle moving at decent speed will hit a man hold cover twice pretty quick. The only thing there is you should hear your sound very frequently, more so during 'rush hour' than say in the wee hours of the night.