2003 Toyota Corolla wet carpets / leaks

After some months, someone pointed out a mildewy smell in my car. Investigation demonstrated a wet carpet on the driver's side back seat area. I've been trying to dry it w/ heat and blow-drying, but every time you press on the carpet it gets wet again, so apparently there must be a small 'puddle' underneath. Question 1: will I need to pull up the carpet or cut it to gain access to the floor of the car to properly dry it? Question 2: Is there a commercially available fix that is reasonably priced. I've been told not to let it continue because breathing in mildew is not healthy. Also, does this condition indicate that there is likely a leak that keeps the water collecting there, and where should I look for that leak. (There is a a sunroof on the car, but in the past, if it is clogged, it drips onto the driver and front seat passenger). Thanks to anyone who can help me