I had the same problem with my Grand Prix. I discovered it when i was installing the deadener. I thought I had a leak at first but come to find out it was just from years of wet feet, open doors during the rain, and condensation. Since water that gets in the car has no way out and if it was able to evaportate it would just recondense in the car, it just collects in the padding. It was wet enough to wring water out of it so since i had it out of the car anyway i just rented a carpet shampooer and it worked wonders. Made the carpet look near new too. No i am just really careful about my feet being wet when i get in and keeping rain out.
