Probably chipmunks. Those critters are responsible for trees growing in weird places from mulch in my landscaping. When the saplings are plucked out, there's always a walnut hanging from the roots.
We've had mice in our new camper already. They wanted the snack chips until I sealed any openings and now store bags of munchies in plastic bins.
Plain ol' traps work well, unless you're like the old farmer woman parked next door who would slap them with her bare hands, like a Whack-a-Mole game. Wow.