When I get up in the morning, there is a vibrating noise from the pipe entering the house and going to water heater and the rest of the house. It's like a tapping. It happens for a few seconds, then stops, and then it happens again. I never hear it after I come home from work. There is a pressure regulator valve at the beginning of this pipe and the noise is between that valve and the separation of the main pipe to the water heater and the rest of the house.