I have the same problem, but, I think I have a rear os door that seems to fill up with water when it rains. I don't know why as I haven't investigated properly yet, but, it seems if I open that door after raining, it runs out. I reckon if I don't open the door regularly, it gets into the car, makes the carpet damp, which in turn causes condensation on the windows. The window motor has packed up on the door too, suggesting dampness etc.