Another “in-wall” issue is caused by a one time ill advised idea of using aluminum wire. If that was connected to brass or copper terminals then the interactions between the metals will be a problem. You you tie an aluminum wire in a wire nut with a copper wire, the same issue will occur.
LIONS have been known to do in-wall wiring and him is NOT up to date on the fire code.
Do not trust what is in the wall unless you KNOW what is in the wall. Someone may have added an aluminum wire to an existing copper branch and an inspector (if one was called at all) might not even notice.
At the moment a certain young felid is howling at my window. I suspect she wants a bowl with some calories in it.
ROAR