Lived in our house 7 years and in last two months have started with an annoying cluncking noise every couple of minutes it comes up through the pipes from the mains inlet. Even when we turn off the water at the mains we can hear a vibration still, not all the way up the pipes but near to the outside mains, can anyone help. We have drained the system checked all units (taps, tiolet cistern) we cannot find where the problem lies. 
