Sound by sound
| Sound | Cause | Fix |
|---|---|---|
| Bang when a valve shuts quicklyMost common | Washing machine, dishwasher, ice maker or single-handle faucet closes; worse with high pressure. | Water hammer arrestors at the appliance; a pressure-reducing valve if pressure is high. |
| Rattle or knock while water runsMost common | Pipes move against framing because straps are loose or missing. | Secure and cushion the pipes where they're accessible. |
| Ticking as hot water runsPossible | Copper or CPVC expanding against wood as it heats. | Often harmless; padding the hangers helps. |
| Whistle or squealPossible | From one fixture or valve. | Open the valve fully, or replace the worn washer or cartridge. |
| Hum or vibration through the houseLess common | Often at high pressure, or from a failing pressure regulator or well pump. | Measure pressure; service the regulator or pump. |
What you can check
Measure the pressure
A hose-bib pressure gauge costs little. Readings above 80 psi make hammer much worse and stress every fixture.
Note which fixture triggers it
Appliances with fast solenoid valves are the usual trigger.
Look at exposed pipes
In a basement or crawl space, see whether pipes can move freely in their hangers.
Why it's worth fixing
Repeated hammer shocks loosen joints, wear valves and can lead to leaks over time. High pressure, the most common contributor, also shortens the life of water heaters, toilet fill valves and appliance hoses.
How plumbers fix noisy pipes
Water hammer arrestors are small sealed chambers with an air cushion behind a piston. Installed close to the valve that slams shut, usually the washing machine box, dishwasher supply or ice maker line, they absorb the pressure spike. Older homes sometimes have air chambers, capped vertical pipe stubs that do the same job until they fill with water; draining the house can restore them temporarily.
If pressure is high, a pressure-reducing valve at the main brings it down to a safe range. On closed systems with a PRV, an expansion tank at the water heater keeps pressure from climbing as water heats.
Pipes that rattle are re-strapped with cushioned hangers. Where they're inside finished walls, a plumber may approach from an access panel or a nearby opening rather than opening the whole wall.
When to call
- Pressure is above 80 psi, or the pressure-reducing valve is old.
- Banging started suddenly with no new appliance.
- The noise comes from inside walls you can't reach.
More questions
Can water hammer burst a pipe?
Rarely by itself, but the repeated shock weakens joints and fittings over time, and combined with high pressure it can contribute to leaks.