We have a tough one here folks. We have a persistant knock in our pipes. This is a single knock that you could set your watch by. It occurs every 3-4 min. and it is a single knock. Nothing is on or running or being flushed. We have had 3 different plumbing companys out.We have replaced water softner, toilet guts, pressure tank.We have a well system. We shut off water valve and we still hear it. We turn the water softner to bypass mode, and we still hear it. We have shut off power to the well,it still knocks. This is not a rattle or banging. It is one single knock every 3-4 min. Please help as this is making me go crazy. I dont know what to do and i cant keep paying people to come out. email@example.com Thanks!!
It sounds like a check valve in the system some place. I would check around your water heater, many of the electric water heaters have a ball check in the dip tube and it knocks also check if you have a hot water recirculation pipe these also have a swing check valve on them. You will want to use a 3/4″ copper pipe about 18″ long placing one end against the water piping and listen through the other end to pin point where the noise is occuring you will have to try differn’t spots unitl you locate the source of the knock.