The Pipes Are Knocking After Draining the Bathroom Sink

Pipe Expansion

• Running hot water through the bathroom faucet may cause a cracking or popping sound to occur. The noise manifests when the pipe that carries the hot water to the faucet heats up. As the pipe heats up, it will expand. When the pipe cools off, it will shrink to its original size. While shrinking, the pipe will make excessive noise. Wrapping insulation around the pipe will help reduce the noise.

Loose Pipes

• When you turn on the water in the faucet, the pipes may start to rattle, shake, bang or clank. The noise may occur if the pipes are loose. The pressure from the water flowing through the pipe will cause it to move and it may start hitting the wall. The vibration of the water inside the loose pipe may also cause noise. You will need to secure the the pipe to eliminate the noise. If the pipe cannot be secured, cushion it with insulation to prevent the noise.

Defects

• Over time, a pipe may begin to whistle when the water is turned on because of a sediment buildup, defective washer or valve. If the washer or valve are defective, you can undertake the task of changing them yourself or call a qualified plumber. If the noise occurs because of sediment, the pipe may be suffering from rust and deterioration. If it is allowed to continue to get worse, the pipe can burst.

Water Hammer

• Excessive water pressure that flows through the faucet's water pipe and is suddenly stopped by the faucet's valve when you turn off the stream will make excessive banging noises. The valve closing will cause the water to stop, reverse directions and reverberate with force back down the pipe. Known as a water hammer, the spike in pressure inside of the pipe can harm a hot water heater, valves, pipe fittings and washers. A plumber will install an arrester in the pipe to help prevent the water hammer.