Strange this is a guess but maybe your drain in the gas cap area is pluged and the gas tube is loose. If that is the case then it might be dripping down the gas pipe to the gas tank which is right behind that carpet. Try poring some water where you put your gas there is a little hole that should drain the water out. The problem I had was when i would open my trunk water would come out of the panels on the trunk lid so thats why I put silicone under my wing. Did you check your headliner to see if there were signs of leaking.