When I turn off the cold taps in my house there is a loud banging noise from behind the wall in the downstairs bathroom (which is where the cold water supply enters the house). This started happening some months ago now and I can't think of anything that happened plumbing-wise just before it started.
Anyway, I found that I can temporarily fix this 'water hammer' by turning off the water supply where it comes into the house and then draining the cold water system by running all the downstairs taps. When they run dry I turn the water back on at the main stop-tap and the banging noise is gone!
After a few days the banging starts to happen again - quietly at first but growing to the loud banging again after about a week.
What could this be?
My guess is that this has been caused by some bracket (or similar) that was holding a pipe behind a wooden wall coming loose. I'd much rather fix the cause and to install an arrestor in an appropriate place I'd have to mess with the wall anyway I think.
The only thing I can remember happening around the time this began was some very windy weather. When I heard the first bangs one night I assumed it might have been something banging in the neighbour's garage, which shares a wall with my bathroom.