I had a bathroom added to my house as part of an addition last summer.
The copper hot water pipe rattles inside the wall; at least it does when the
valve under the sink is not fully open. My wife likes to turn it down
halfway or so. When the valve is half closed, running the hot water in the
sink cause the pipe to emit a loud "chatter" in the wall. The contractor
who did the job, and his plumbing subcontractor, have apparently told my
wife that the valve should be open all the way for normal operation. They
say of course the pipe will rattle when the hot water valve is turned down.
I suspect the pipe somewhere inside the wall was not properly secured. What
is the real story here?