Near the end of the winter, I noticed an occasional pipe knocking sound, which sounds like a loose pipe hitting wood. With finished walls and a finished basement, I can't locate the source of noise. Too date I've tried a couple of fixes:

1. Drop the pressure using the inside regulator. The gauge I used was so-so, but I think I dropped the water pressure from 55 psi to 45 psi. The pressure was fairly solid, now a bit diminished but still ok. That seemed to take care of the problem for a week or so, then it came back.

2. Turned off the main water valve coming into the house. Opened the highest and lowest faucets to drain water for 30 minutes. Closed the lowest faucet, refilled the pipes, let air out from all faucets. Again, this seemed to solve the problem for a few days, then a week or so later, I can hear it again.

House built 1998. Mostly copper pipes. PVC pipes used in the bathroom of a finished basement. Gas water heater with no pressure tank on it.

Anything else I should try? I'd rather not start popping holes in the wall

Thanks
Bruce



Edited 1 times.

The mystery here is that after draining and refilling, it was silent for a few days. But your installation includes both copper and PVC material. PVC expands more than copper. I once had an ABS (form of plastic) waste pipe that made a popping sound as hot water was drained through it. It turned out that there was no room for expansion, it expanded to rub against the wood joist or plate and this expansion caused the pipe to make the sound which was annoying.

Was any construction done, just prior to this noise starting? Even something you might think is unrelated.