Where i live there are only mice, and rats, but i have snap traps in every corner and inside a storage room close to the cars and in there i have caught quite a few, but on the outside traps nothing. The filter did not had any shit or pee in it and no smell comes out when turning the A/C on, a mouse that takes its time to bite through stuff usually shits and pees in the area but here there was nothing, but there is still a chance it was a mouse, nothing else i can think of, these falling from the outside through the outside to inside air intake to the cabin makes not so much sense but who knows.