[SkykingUSA]

I had the same thing, but it just wiped off with a good cleaning. I believe it's just the natural spot where water runs down the car between the doors. It looked like water stains to me the last time I washed it. I think it just shows up more than normal because it's against the shiny black bits.

When I first got my car, it was the worst (hardest to get off), probably because it had been caking on since the car was built and started being transported. Once I washed it off the first time, it seems to come off more easily now when I wash it. If you look closely, you may also see it under the other ends of the side doors too, not just in the middle between the doors.