Thread: Knocking Sounds in Drain Pipes

Wow never heard of that. I guess now test with cold water only and hot water only.

It will make the noise with cold water only but not near as much. If you run cold for a bit then hot it will get fairly loud. I'm thinking this video shows what is going on...it's very weird...and I might run it by a plumber just to get a professional opinion...that's not to undermine the vast knowledge of CDC though....

You may need The Exorcist.

I would say depending on how warm you keep your house the pvc may still pop with cold water. Is your heating ducts near or right next to your pvc. Anyway your pip is probably rubbing on something when it expands and contracts. I have a sink in my basement that does this.

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The pipe may be tight going through the wood to the point that you are hearing this expansion and contracting of the pipe.

I have had to repair this problem several times in new homes. It is the pipes expanding lenghtwise (getting longer and shorter) as the water heats and cools the pipes. Usually hot water causes the most problems. The pipe will pop rapidly as it gets hot and then pop slowly as it cools when the water is shut off. It may take an hour for the pipe to cool. The problem usually occurs where the pipe penetrates through the top or bottom plate(2x4) of the wall and is caused by the pipe rubbing on the plate or a metal fire stop around the pipe if used. You will have to open the wall and cut the hole around the pipe looser to allow it to move. Sometimes you can just slip a piece of card stock or thin cardboard (cereal box) between the pipe and the plate and this will allow the pipe to move without binding.It's a PITA but it's better than listening to the pipes pop for an hour when you are trying to go to sleep. Good Luck.

PVC POP!!! Ive had it in our condo for 25 yrs, Plumbers wont touch it, say its not hurting anything, no leaks etc. Live with it. You used PVC instead of solid metal.

Thanks for the replies I'm convinced now that it is just expanding and contracting. I might try to stick some cardboard or something around the pipe to see if that helps. I was more concerned than annoyed. If this is my biggest problem in the house then I'm doing pretty good, knock on wood. My last house was pretty old and had copper pipes. In the garage the pipe that drained the kitchen sink wore through and leaked. Nothing J.B. Welding didn't fix.