Also make sure its not a condensation sound(vent contensation driping on burner makes loud banging sound)also corroted or mismoved flue baffle intank makes noise
You have to isolate the problem, find out which fixture makes it happen , if all of them you have to inspect the piping there might be a bad check valve or prv .
Thanks guys for all the advice you given so far.
In 2-3 months i open my company,does anyone have a mainline sewer camera with monitor and locator for sale or recommends a good but cheap one inline to start?
Lol,
i think im just tired of wasting time and hearing clients want to repaire theyre 20+year faucet/valve,since i started geting more firm on my presentation i hardly get objections to complete faucet/valve.replacement