Hi guys/girls , can any body help? , i have a loud water hammer noise ,(like a fog horn) mainly at night,( when nothing is on) (and normally occurs twice within 30 seconds of each time) i have ;;; turned heating off , reduced pressure/ increased pressure, i have checked and replaced ball cocks in the loft, i have replaced stopcock , there is no connection with water running when this occurs, i have even heard and felt this noise on the rising main in the house when this happens,,, , no ball valves are leaking anywhere, toilets are all good.... has any body any ideas? i cant see the point in fitting a prv valve or dial ,, two months ago we had a water issue in the village , could this be connected? any help or advise would be appreciated . thanks mark