No leaks on the overflow pipe and the last time I peeped my head into the roof I saw that the drip tray was bone dry.
I have slight water hammer on my cold tap in my garage, and the hot tap in the en suite bathroom (opposite side of the house) will splutter in a very strange way - if I open the tap half way, the water will flow until the water starts getting warm. Once it's hot, the water flow stops. If I then turn the tap open another 1/4 turn it gushes out as if I opened it full blast - however, I do think this is a tap washer problem but stand to be corrected.