My shower always had a bit of water hammer at certain temp settings. I changed the leaky old tub spout, thus changing the length (and resonant frequency) of the system slightly. Feels like it made the water hammer (more of a buzz) at certain temp/pressure settings worse.

Putting a plastic gasket behind the tub spout reduced the problem, but didn't totally eliminate it. Any suggestions to get rid of the issue entirely? The vibration can't be good for the copper pipes in the wall!

Accessing the pipes would require cutting a hole in the kitchen wall (the wall on the shower side is tile over brick!) so hopefully that won't be needed.