When I shut off the water I get a Fog Horn sound coming from my pipes. I can not tell where is really coming from as a I heard it from from all over. It does not seem to any certain faucet that causing the problem, I have heard it from the upstairs shower, upstairs kitchen sink, downstairs bathroom sink and even the laundry which is also downstairs. I have read several post here about knocking and I would say it is not a knocking should but more like a fog horn or a tuning fork.

The home is about 6 years old and is on the market so I need to get this fixed. Any ideas would help greatly.