Help. Water in ac/heater fan housing

I need a little help here. When changing out my ac/heater fan, I found about an inch of water in the fan housing. Carpet was also wet (just rained pretty good). Where could the water come from and how do I fix it? Thank you in advance! 1999 Tahoe 2 door.

My 1996 does the same thing. Anybody have any ideas.

This can happen for a couple of reasons:

1. Leaky bottom windshield seal.
2. Under the cowl, there is a plate that the sealant can come loose on. You should be able to add some clear sealant to block it off.

Also check to make sure the drain for the heater core is not plugged.