I'm having a water hammer issue and have for the past year or so. The only new addition was the GE HE washer. We have 90psi as water enters the house. I put in a whole house pressure regulator and have it regulated at approximately 70psi. I occasionally see it at 75psi. We have a whole house Pelican water treatment setup in our house because our water is so bad. When we do laundry I get water hammer noise when the solenoid closes. There is no expansion tank on the water system. I installed a regulator on the cold side of my laundry spigot hoping it would help. It is set to 40psi and we still get hammer. When the icemaker shuts off after filling you can hear the solenoid closing hard but no water hammer, same with the dishwasher. There is a 4' tall 3/4" air arrestor tube just as the water enters the house. The laundry spigots have air arrestor tubes attached to the spigots as well, as do most if not all toilets and sinks. When the house was built in 1989 the plumber added them. I'm sure there is further info you need but I'm not sure what, ask and I'll answer. Any help or suggestions would be appreciated. TIA Pete