House is two story, eight years old, pipes are pvc. Problem started in the last month. Anytime water is cut off in house pipes seem to moan or, as my four year old calls it, hum. (Maybe the pipes don't know the words.....) The noise just slowly fades away after about a minute or two. It seems to be happening more often, running washing machine or dishwasher, shower, any faucets, etc. One interesting tidbit, turn off shower(upstairs)and noise starts, flush toilet and it ceases.

 

Usually moaning pipes are indicative of a faucet or valve washer that is loose, and as water flows past the washer, it vibrates and creates the moan. And, usually this can be isolated down to a single valve or lavatory, shower, etc.

However, based on what you are saying, it happens after ANY use of water in any room. I would start paying attention as to whether it is Hot or Cold, I am betting on Hot. And I would find the source based on what lines were in use when the moan started. If it is ALL hotwater lines, the first valve I would take apart is the first valve coming out of the hotwater heater.

The other major cause is water pressure that is too high, so let us know if you have measured it, or have ability to reduce it.

Let us know what you find.