We had a bathroom built in our basement. The inspector told me the pump was huge and overkill for the one bathroom but it passed. When you're in the shower you here a loud bang that sounds like someone banged on the wall really loud. Went around to the pump and when the water runs for a while you here it swish through the pipes all at one and then there is a loud bang that actually shakes the wall that the shower is on. Is this normal? I am worried since I fired my contractor for numerous reasons including using an unlicensed plumber.