Why is carpet constantly wet in my car?

96 pontiac Grand am. Carpet constantly damp, more so on right side than left. Independent of weather (rain). No leakage from seals around doors as checked that. No holes in floor either.Don't think it has anything to do with rain or outside moisture. Everything else works okay, just getting to point that carpet is smelling little musty. Heating and a/c works fine. Been watching radiator coolant level, and appears to be steady, possibly slightly less. Anyone have any experience with this problem?