Question: "I have a leak and I think it's coming from the bottom of the driver's side door. When I have the door open I can hear it sloshing around."
Answer: It sounds like the drainage holes are probably blocked. Water will leak down inside your door from the window, it is supposed to. From there it is supposed to drain through holes in the bottom, if not the bottom of the door will fill up with water until it reaches a level where it can push past the inner door membrane, where it will get inside the car and make your carpets wet. The best way to fix this is to have the door apart and clean it all out, but remember to properly reseal the door membrane afterwards, or you will cause yourself another leak.