I just had this problem approximately a month ago. My Altima sat in the rain and soaked a box I had in my backseat footwell on the drivers side.
I took the car to the dealer, and they found that my windshield wasnt sealed properly at the factory, and so water was coming in behind the drivers side A Pillar. It completely soaked the carpeting on the drivers side (front and back).
The dealer ended up replacing my windshield and removing my entire interior so they could replace the carpet and padding.
2008 Altima 2.5SL w/CVT
Navy Blue w/Charcoal Leather
Mods: Sirius S50 Radio
Wanted Mods: OEM Fogs, K&N CAI, Stillen Cat Back Exhaust