I have a real water hammer problem, and the arrestors I've installed aren't working. I have a newer bathroom in my basement, below the bathroom in the floor above. I first noticed it soon after we installed a front loading washer. I hear the hammer in the ceiling above the basement bathroom (all the pipes I can see are well secured). I can make the hammer go away if I drain the system, but it always comes back. And -- here's where it gets weird -- if I shut off either the hot or cold water valve that feeds the basement shower, the hammer goes away completely. My plumber installed hammer arrestors above the shower -- didn't work. I also put them where the washer connects, no help. My plumber is stumped. He seems to think that a pipe isn't secured properly. But that doesn't explain why closing the hot or cold water valve to the shower stops the hammer. Help! Thanks in advance... Brian.