Bud – you are a genius! The problem had nothing to do with the water heater, it was an outside faucet that had been left on (connected to hose and sprayer) that had built up pressure over a few days. Amazing how those sounds can seem to come from everywhere….including a perfectly functioning water heater. Thank you so much for pinpointing the problem even with my off the mark description. I have you to thank for the good nights sleep that Ill be getting. THANK YOU!!!: Dana Nosleep: If the noise is a non stop situation (with the heater turned on or off), call the Water Department. It may be caused by a pressure reducing valve in the supply service to your home. It could be a noise being produced by a recirculation pump if you have one or other appliance in your or a neighbors apartment(if you live in an apartment building) : I would try the Water Dept. first….Bud.