My 2009 Nissan Altima Coupe, 2Dr, 100k miles is accumulating puddles of water on the rear floor, passenger side. This only happens when it rains. I put a towel down to help soak up some of the water. There were spots of rust color on the towel. None of the seats or side panels were wet from drips. I also had a mechanic poor water outside of the car, down the side passenger door and over the sunroof, but there were no drips on the inside from the door/window/roof seals. Has anyone else had this problem? Do I take this problem to a regular mechanic or a specialty mechanic?