2002 Jetta Water Leak?

I have a 2002 Volkswagon Jetta and I believe there is a leak but I'm not sure where. The driver side and passenger side floors are always wet when it rains, the entire car gets a musty smell. The speakers also crackle occasionally when it rains and a few days afterwards...I'm thinking its water. I don't see any actual dripping or leaking. A friend of mine said it could be the windshield wasn't sealed properly and that could cause it. Any ideas of what it could be?