Hi,
I am no professional but I dont think this problem is water hammer...the noise comes and goes at any time, never when a toilet is flushed or taps opened.
In fact the noise has started being more frequent at5.30am!
The noise is coming from the back bedroom chimney breast wall, its a thundering noise , which can be heard from downstairs, lasting maybe 5 or 10seconds This is driving me crazy, any comments would be greatly appreciated. Had a new radiator put in the dining room,with a new boiler about 5 months ago, but I think it may be started before then.