One other item to add to the other posts... last winter I had a similar problem, that I attributed to my kids tracking snow on their boots into the car. As a result the carpeting under the floor mats became wet and it took me quite some time to dry them out. It also caused my car to smell like a swamp due to all the moisture that was trapped in the car. This year my solution was to purchase rubber mats that hold more water before they overflow and get the carpeting wet, that and the habit of kicking snow off boots before entering the car.