water flow noise and leak

hi. The house I live in has a tennanted apartment above me. I own the house.
When my tenants turn on their tub/shower, the sound of the water flow through the pipes in the walls is quite loud. I've tried clearing the air out of pipes and that helps a bit but only for a few days. The flow noise seems to be the problem. This doesn't happen when they turn on their kitchen faucet. However, their lever-style bathroom sink faucet causes a single clunk when it is turned off rapidly. This isn't typical water hammering since I've purged the pipes repeatedly to no avail.

This flow noise doesn't happen when I turn on the water in my bathroom or kitchen or laundry area. Same water supply.

I believe this all started when I replaced the tub spout with a Moen add-a-shower diverter spout from Home Depot to allow the use of a shower head. I also retiled the backsplash around the shower tap/spout at that time. In addition, at about the same time, I've noticed a very slow leak indicated by a spot on my ceiling under their tub area.

Is it the cartridge? it's an old Moen single pull-knob type of tap. Is it from the diverter/spout? Is it related to my pipes perhaps not being well secured behind the spout (I think not as when I screwed the spout on with teflon tape, the pipe felt like it was snugging up towards the back of the tile)? Maybe the cheapish Ikea bathroom faucet and/or it's cartridge? Is the pressure too high? Do I need an aspirator (not sure how those work)? I'm at a loss.

Any advice would be appreciated.

noise

quote; This isn't typical water hammering since I've purged the pipes repeatedly to no avail.

It IS typical water hammer. "Purging" the pipes does absolutely NOTHING to eliminate water hammer. In fact, if there were air in the pipes it might PREVENT the water hammer. As for the noise, it could be caused by turbulence in the new spout you installed, if the noise did not happen until then.

There is no way air can get into water pipes except when they have been drained. In that case, when the water faucets are first opened, the air is expelled. Other that, the pipes are always full of water. Look at what you replaced as the cause of the problem.

When you replaced the tub spout, you may not have achieved a good seal, and when the pressure from having the divertor on is present, it leaks in the wall. It could also be a problem if it is a 'push-on' spout, that you damaged the o-ring when installing it. Put in a pair of hammer arrestors under the kitchen sink, and the thunk should stop. Some diverter spouts can create a whistle if they don't seal properly which is very annoying. Only real option is change it for a better one.