There can be a number of causes of the noise and these should be investigated. A “thumping” noise may be experienced whenever a hot tap is turned off suddenly. This only occurs if a non-return valve is installed. The sudden stopping of the water flow at the hot tap causes a small “energy wave” to travel back down the water pipe. This “energy wave” generally diminishes but if a non-return valve is installed, the energy comes to an abrupt halt causing a “thump” to be heard. This is a form of water hammer.
A continuing light vibration or whining noise may be heard if there is a defective tap washer in the tap housing. Replace the tap washer. A continual tapping or knocking noise may be heard when a tap is running. This is water hammer. It occurs when long runs of hot water pipe are not adequately fastened inside the wall, ceiling or floor cavities, and results from the pipe vibrating against a wall, ceiling or floor cavity as the water passes through the pipe causing it to resonate. This is overcome by securing the hot water pipe, to prevent movement.
If an electric water heater is installed and noise is evident only during the heat-up cycle, check for mineral build up on the heating element and check the quality of the water supply for sludge. Clean the heating element or drain sludge from the water heater if required. If a noise is evident only when water is flowing through the water heater, and if it’s not water hammer, then check for restrictions in the pipe work or for faulty valves. It may be necessary to install a pressure limiting valve if the water pressure is excessive (above 700kPa).
All storage water heaters are essentially a vessel filled with water with no moving parts. Therefore, it is unlikely any noise in the hot or cold water system can be attributed to the function and performance of the water heater.