Not sure if you're keeping up with all my post. But if not see Random Noise in Pipes, Random NOise in Pipes - Expansion Tank, etc... Tonight we turned our water heater to pilot. And we still hear the noise. So now we know that it is not the water heater that is encrusted with junk. We know it is not the expansion tank. So, when we were in our utility room waiting to hear the noise we noticed that you can hear the rumbling in our ducts. We noticed that our furnace kicks on, then a few minutes later the fan starts, then the furnace seems to quiet down but the fans still goes, then the fan stops, and sometimes we hear the noise. I put my ear to the duct and you can hear the "Noise". Now, I can't say that it is the furnace or maybe our duct work is sitting on a pipes causing the noise to seem as if it is coming from the pipes. But we are just so lost. Does anyone have any ideas??????