Hi all, I need some expert advice in diagnosing the problem I have been having for a while. Whenever I open a tap (hot mostly, cold sometimes) or close a tap , or when the toilet stops flushing, or when the washer starts fill or stops fill I hear a knocking noise from behind the wall (upstairs room). I also hear the same noise at the PRV. I did some pressure tests and the high pressure was 78-80 psi, static pressure around 70 psi. I did call a plumber and all he kept saying was maybe the pipe is loose and cut open a piece of drywall but didn't see much, and he wanted to cut more drywall but I told him to let it be. Any idea if it's perhaps the pressure too high causing this or is it infact a bad PRV that needs to replaced or is it really a loose pipe somewhere? I am not sure how old the PRV is because the house predates me. Any help would appreciated. Thank you, JB.