I have a Grundfos PC-15 Presscontrol Pump that runs all my house water. When I flush the toilet I get an awful clunk sound at the start of the cycle. As the toilet take a while to fill up, the pump cycles on and off 4 times, making a clunking sound each time. This only happenswith the toilets, and not with any other use. Grundfos tell me that there is a metalstop valve built in the pressure control unit which is making the noisem which is then being amplified up the copper pipes?? On advice I have inserted a lenght of plasitic hose after the pump in order to try and reduce the sound running up the copper pipes. This has not worked very well to date. Is there anyway in changing the toliet filling system to stop this clunking? or any other advice??