To stop water hammer, drain and refill the home's plumbing system. Shut off the main, and then open taps on the highest and lowest floors to drain all the water. Then, close the lower tap, turn the main back on and allow the plumbing system to refill to the top.
Water hammer occurs when air chambers built into the plumbing system become filled or blocked. Normally, these chambers help mediate the pressure buildup caused when taps close. When they become blocked, that pressure can resonate through the pipes, creating a distinctive hammering or growling noise. In extreme cases, this can loosen plumbing joints and fixtures or cause other damage.