A: Everybody who has complained about something like this eventually found a fixture somewhere that was locked open. Possibilities include the temperature/pressure relief valve on the water heater, and things like washing machines and dishwashers. You may be able to check the T&P by seeing where the drain line goes and checking for running hot water there. The other places involve process of elimination. -- Randy

A1: Check the outdoor hose?

A2: I found my leak just outside the water meter sump at the street. The female PVC adaptor was cracked. The water was able to channel down to avoid disclosure. No water ever showed up above ground. I turned off the main valve at the house and the water meter still showed flow. David

A3: Might I suggest you feel both the hot and cold lines above the heater? If nobody has used water recently and the cold inlet really is cold, then water is running through the heater. If it isn't leaking through a fixture, than it's leaking from a (possibly buried) pipe. Turning off the cold inlet to the heater will give you a clue as well. If closing the valve stops the noise, this confirms there is a leak downstream, in the hot plumbing. As Randy said, the relief valve can cause this problem too. Larry (9/30/07)