I cannot figure out this pulsing/thumping in my water line. It can be felt on the incoming line from the house and make niose at the hot water heater. Can be stopped if I turn a shut off valve before the hot water heater. Before the shut off it splits to other portions of the house such as tiolets and faucets. It isn't constant but goes for 20-30 seconds then off for a minute. I already closed all the tiolets shut off valves at the tiolet and it still thumps. I have a 40 gal. water heater w/ expansion tank, no backflow preventor or regulator, city water and 85 psi pressure. Driving me nuts.