Thank you! Will probably be changing toilet parts next... But, last night we drained the pipes. Some change. Sounds are somewhat less frequent. Pipes are really groaning rather than hammering now. Our house sounds haunted! :) We have had a suspicion that a toilet has been slowly leaking at the base, around the waxy seal...but there haven't been noises other than those with water usage. And, though I had seen the cold water pipes vibrate, with last night's draining, there is clearly sound when we use the hot water now, too. (I have not had a chance to look at the hot pipes when they are making noise, so not sure what is going on. Water heater is not even a year old, and there were some noises before installation.) Any other suggestions? Go ahead and change the tiolet parts, still? Thanks again.