: : I have a new bungalow with 2 bathrooms in it. whenever I flush either toilet after the bowl is clean I hear knocking noises coming from the stack. I have had the builder send their contractor out and he is trying to tell me that the noise is because of the plastic pipes and that's the sound they make. What I am wondering is if anyone else has had this problem and what the real reason may be so that I can go back to my builder to get this issue fixed.

: : any help would be greatly appreciated.
: : James; One possibility is a loose hanger on the vent pipe riser, or not enough hanger clamps. Also it could be the supply water line to the toilet not anchored securely. Keep after the builder,and he will keep after the plumber to correct. Hube

The plumber has so far cut out and redone all the stack, made sure the pipe is not touching any of the joists and anchored them and the noise is still there.

I am just looking for other ideas since the plumber is convinced it is "water noise" and to me water noise doesn't involve a banging noise when the toilet water goes down the pipes