Grass in my blower fan

I live in North Dakota and have a 1994 Buick LeSabre that sits outside. Something keeps stuffing the blower motor full of grass. At first I thought it might be mice, but I set up some traps and caught nothing. In fact after a couple weeks the traps disappeared from under the car. If I leave the car at my office it seems to get left alone. Could this be a squirrel? How do I stop this?

It could be almost anything.  I had something like that once and I set up a video camera.  It went over five hours of an 8 hour tape one night when I found out it was a rabbit.

My bet is a raccoon. Nothing smarter than them.