I have a 2005 dodge Durango limited edition. I just recently took it to clean it out and when I took out the matt on the passenger side, the carpet is soaked. what could be wrong with it?

 

Leaking heater core, clogged AC drain, leaking window/door seals. Start checking those things.

 

I noticed mine was leaking when I pulled the passenger side seatbelt out all the way. The portion that was down near the floor and normally stayed rolled up was wet. I pulled the door sill off and could see water. Then I found the carpet wet. I blew out the sunroof drains and could see they were clear. I caulked the mounting holes for the roof rack and still got water.
I dried out the entire floor and channel under the passenger side door sill plate (plastic pops off easily). I then placed a hose on top of the truck and let it run over the sunroof and down the passenger side door area. I sat inside with a flashlight and found water appearing in the channel under where the door sill had been. It turned out that the water was pooling in the gap between the door and roof and getting underneath the door seal. I removed the door seal starting at the top and I went about 1/2 way down the sides. I put a very small amount of gasket sealer on the rib of the door frame that the seal slides onto then put the seal back in place. No problems now for almost 3 yrs. I hope yours is that easy.