Every time my washing machine switched from fill to drain, the pipes behind the wall let out a bang like someone hit them with a hammer. It scared guests. It annoyed me at 2 AM when I ran a late load. The plumbing term for this is “water hammer,” and the fix is one of the easiest DIY repairs I have ever done.

What causes water hammer

Water is heavy. When it is moving through pipes at pressure and a valve slams shut — like when your washing machine or dishwasher finishes filling — all that moving water has to stop instantly. The momentum creates a shock wave that rattles the pipes. The bang you hear is the pipe physically hitting the wall or framing inside the wall because it is not secured properly, or it is the shock wave itself echoing through the plumbing.

The 10-minute fix

The device you need is called a water hammer arrestor. It is a small cylinder, about the size of a D battery, that screws onto the water supply valve behind your washing machine. Inside is a piston or a bladder separated by a chamber of air. When the water slams to a stop, the shock wave pushes against that air pocket instead of banging your pipes.

1. Turn off the water supply valves behind the washing machine. Both hot and cold.
2. Unscrew the hoses from the wall valves. Have a small towel ready — some water will drip out.
3. Screw the water hammer arrestors onto the wall valves. Hand-tighten, then give a quarter turn with pliers. Do not overtighten — the rubber washer inside does the sealing.
4. Screw the hoses onto the arrestors. Same hand-tight plus quarter turn.
5. Turn the water back on. Run a short wash cycle and listen. The bang should be gone.

Water hammer arrestors cost about twelve to fifteen dollars a pair at any hardware store. Total time: ten minutes. This is not a temporary fix — they last for years.

If you still hear noise

Sometimes the problem is loose pipes in the wall, not water hammer. If the arrestors do not silence the noise, the pipes themselves need to be secured with pipe clamps — which usually means cutting into drywall. But try the arrestors first. They fix about 80 percent of noisy pipe situations, and they are cheap enough that there is no reason not to try.