I have a water hammer issue mainly affecting two bathrooms, one directly above the other. The hammer is present when both toilet valves close, when closing the cold water on both sinks and when closing one of the shower valves. I added arresters to the washing machine about 10 years ago and it seems fine. When the house is quiet I can hear the shock wave moving back and forth until it dissipates. I originally thought I had unsecured copper pipes but have ruled that out. The normal water pressure is 58 PSI. I can easily access the 3/4 copper right before it splits to the two bathrooms. Would adding a single arrester at that point accomplish anything? Or will I have to add arresters at every fixture?