Thanks everyone for the replies and ideas. It turned out to be an electrical box which I believe may go along with the stereo amplifier that was installed. It's just a rectangular box with wires coming out of it. No drugs, no rock or jack damage, no dead mouse, and no money. I ended up moving it closer to the sill so it's not right in the middle of the floor. Since I had an idea it had something to do with the amplifier and I had looked under the car and found no damage, it really wasn't driving me that crazy not knowing for sure.