Everytime the new power vented gas water heater cycles on, there is a knocking/clicking sound that comes up every four seconds or so which appears to be coming from the 3" PVC exhaust pipe from the water heater to the outside. I am guessing the hot air is expanding the pipe, but I don't know what to do about it. In fact, I don't even know who to call to make the repair. A plumber, HVAC guy, General contractor or someone else. Can somebody help me out?
Call your HVAC company. Most likely water from the exaust getting in the way, but nothing to mess around with if you are not farmiliar with the system.
Let us know what it turns out to be, it just might helps others.