Hello, hope this isn't too long of a read, but I was curious what everyone thought about this situation: During turnover, rather late, I noticed the tile of the shower was cracking along the grout lines, and I noticed it had some give when I pressed the walls.

You could add insulation between the walls but that will not stop vibration.I would tell tenants not much you can do. people have the same issues in apartments.

Maybe some wall units instead?

The problem with this, is you don't know the extent of the damage concealed behind the walls. 

Mix FOOD color with tap waterb.

Who doesnt run their pex on the outside of walls and cabinets....lol

New walls and closet going up

In most cases, the HOA is responsible for anything outside your walls and you are responsible for anything inside the walls.I would pay the bill to ensure the utility is good, then go after the HOA.

We hired a GC for an exterior back wall stabilization.

It is full of mold and the pipes leak from the basement all the way up into the walls.