Do you notice it dripping in anywhere? Or is it just wet and puddled?
If it is wet with no signs of dripping, pull back the carpet and look for water marks in the dust. Usually you will be able to find a clean spot somewhere and that will lead you right back to the source.
It is very likely that it is the weatherstripping in the door. Maybe not the long piece that runs the full length above the doors, but the one that goes around the frame. They join together in the lower front area.
The weatherstripping flattens out over time and will lose it's seal.
If it is none of these or maybe one side is more wet than the other, it is leaking elsewhere. The matting used underneath the carpeting has an amazing wicking ability. There have been many times I've chased a water leak where I thought it was in one area but was actually in another.
Also, be very sure to dry out the carpet before you put everything back together. When you get the leak fixed, leave the carpet pulled back and allowed to air dry if possible.
Good luck
