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!