On 02/02/2021 16:35, Geo wrote:
We had the same trouble a couple of years ago - did all the usual
things without being able to track it down to anything in our house.
Decided it started coincident with some plumbing work in the adjoining
house where a downstairs loo was added - probably with sharp shut-off
taps and valves.
Our mains water pressure is quite high so I fitted a regulator and a
shock arrester just after the internal stopcock.
This improved the hammering but did not completely eliminate it.
A couple of weeks later the plumber re-appeared next door and the
noise has never come back - guess they were suffering too.

Picture here - was just a straight pipe on the left (stainless steel).
https://ibb.co/L80PZfK


Thanks, Geo. I think that must be the situation here, too. Sod's Law, it
hasn't happened since - but when it does I'll be searching outside.

Our water softener must damp the house - but the drinking water feed
comes off the main before it feeds the softener. The amount of energy
going into the vibration points directly away from the house - and it
was audible outside the house.

PA