Noisy pipes can be caused by water heater problems. When you start hearing noises in your water pipes, they can be caused by air or lack of air, obstructions, and clogs in your water line. Here are some steps to take to identify the problem.
Step 1 - Water Hammer
Water hammer is a clunking sound that comes from sudden pressurizing of the water line caused by quickly turning off a faucet or other water valve. Water backs up quickly causing a loud hammer noise in the pipes. This damages the pipes over time. Water hammer events only occur when water is not running. You can rule out water hammer if you hear the noise while you have water running. Turn off the water supply to your home and drain the water from your lines by turning on a low faucet, like an outside faucet or a tub. Close all faucets and turn back on the water to your house and turn on a faucet then shut it off. If you do not hear the clunk noise then a water hammer was your problem.
Step 2 - Moaning or Humming Noise
Toilet ballcock - A damaged or bad toilet ballcock typically causes this problem. Turn off water feeds to all toilets in your home. If you no longer hear the humming noise then turn on each water supply valve until the sound comes back. When the noise returns then the ballcock in that toilet needs to be replaced.
Faucet washer - Washers can go bad in faucets. To determine which faucet washer may be bad, turn off all faucets in the home and turn on one at a time. The troubleshooting is easy. If the sound occurs when a particular faucet is used, the washer may need to be tightened by screwing it tight, or replacing the washer. If you tighten the washer and the noise is gone then that resolved the problem.
Third party faucet stem parts - If you have replaced faucet parts with OEM parts instead of manufacturer parts the fit may not be perfect and can cause air to leak into the system causing humming.
Step 3 - Hammering or "Machine gun" Rattle
Major appliances that use water, such as a washing machine or dishwasher, have solenoids that can go bad. When this happens the pipes may sound like they are rattling or banging. Testing this theory can be done by filling an appliance with water to see if the sound starts. Test each appliance individually to narrow down the source of the problem and get the solenoid replaced in that appliance.
Step 4 - Other Sources of Noises
High water pressure coming from the city or from your well can cause the pipes to buzz or moan. Water pipes may rattle in the walls because they are not strapped properly to the support beams or if the holes drilled to pass the pipes through the beams are too small or not centered. A very rare reason for sounds in your water pipes can come from the pressure regulator. This can be determined by pounding while water is running; if it is throughout the house, adding more water flow changes the speed of the sound.