Does it taste more metallic / acidic or is it more earthy/ sweet?
we live in the country so critters find their way in.
they must have used those metal heat ducts above that
wall and maybe slipped and fell down, or jumped thinking there was something good
to eat on that "plate" ....lol
funny thing about that area, we have a cat that stays on the main floor, and every once
in a while he'd venture down while we were doing laundry, and sometimes he'd stay for a little
while until we realized it and let him back up. he had been scratching the sheetrock on the outside
of that area of the wall, just above the baseboard molding, now i know why!
Those meeces are tricky. I was working on my propane boiler and found two well-toasted meeces in the exhaust flue.
I have no idea how they got there, or how long ago. I would swear it isn't possible for them to get into that flue.
I think they are long gone. The problem was very apparent at one time and someone fixed it but did not go to the extent of ripping out walls.
One thing about rodents: If they thrived there once they will be back. I suggest you take steps to limit their numbers. You need to encourage those that prey on mice to stick around.
Here we have lots of snakes. I encourage and even import the nonvenomous varieties. Not sure what you may have there. You may need keep traps baited or a rodenticide about to keep the numbers down. This has some problems associated with it. Since you have a cat and perhaps some other pets, chemical solutions are potentially problematic.
Whatever the previous owners did will not last forever. Hopefully they sealed the entrances so you won't have to worry about that.