I always thought the main problem in noisy plumbing was the rigid attachment of the pipes, whether plastic or copper, to the wooden framework of the house. The paneling, whether wall, floor or ceiling, would then served as a diaphragm to radiate the sound of water rushing past restrictions (like joints and valves) into the room. The solution, if that was the problem, would be some sort of foam lined pipe hanger or equivalent. Am i right?
What really got me thinking about all this was an old house we lived in with hot water heating and big old 2" cast iron pipes feeding the old fashioned cast iron radiators. When it first heated in the fall after summer the clanking was startling, but it was these pipes forcing their way through their hangers as they expanded, and this was amplified by the floor.
