Hi ptot,

What were their suggestions and how much are they charging you? Is this a new constructed or remodeled house? Is this a new problem? How long have you lived in the house? It should be pretty clear that you are looking for pressurized water finding its way into your drain system which may be partly obstructed. Your also getting water hammer when your valves shut which means the water velocity is high because of a leak of some kind. That is all my crystal ball can tell me with out more info. Aloha.