I need some help from some experts.
We recently had our bathroom remodeled including a new shower with a single valve. We started noticing some water hammer coming from the shower whenever the toilet shut off after flushing, or the bathroom sink was turned off and on. This happens when the shower is turned off. At first I thought it was a defective cartridge, so we replaced that. We also had water hammer arrestors placed on the sink pipes as well as the shower pipes. Noise was still there.
Recently, I discovered that if I shut off the hot or the cold water at the shower valve (there is a shutoff screw for both the hot and the cold water at the shower valve, for maintenance), the knocking stops.
Does anyone have any idea what the problem could be and how to go about trying to fix this? I don't want to have to put the wood trim off from outside the house unless I'm sure I can fix this problem.
Any help or comment would be appreciated.