The energy from the water transfers to the pipes, making them bang around. Removing air from the pipes can help alleviate the problem.
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Check the water pressure in your house. Turn off all other water sources in your home. Remove the hose from the cold water faucet for your washing machine and attach a water pressure gauge to the spigot. Turn the spigot on and write down the water pressure.
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Remove the gauge from the spigot and look at the reading. Water pressure over 60 psi could be responsible for creating water hammer. Water pressure over 60 psi can also cause leaks and burst pipes. The situation should be remedied immediately by having a pressure reducing valve installed where the main water pipe enters your home.
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Check your pipes for noises and leaks, starting with the pipes closet to the water inlet in your home. The hammering sounds might be caused by two pipes hitting each other from the force of the water being shut off. Sometimes the straps holding the pipes to the framing come loose, allowing the pipes to bang together. If the straps are screwed to the framing, tighten them using a screwdriver. If the straps are secure but the pipes are still hitting each other, put a piece of foam rubber between them and see if that eliminates the noise. Use plastic zip ties to secure the foam to the pipes.
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Listen again for hammering noises. If you still hear banging, you may have air pockets in your pipes. To remove the air from your pipes, turn on as many faucets and outlets as possible to increase the demand on the water supply. Let the water run for a few minutes to push the air out, then close the outlets and faucets one at a time. Do not turn off all the valves at once or you may cause a pressure surge.
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If none of these remedies help, you may need to install a water hammer arrestor. These devices have a chamber filled with air or a spring mechanism that absorbs much of the water's shock force when the water flow stops. It's similar to the way a shock absorber works in an automobile.