My 2003 X seems to get a real fine black power that accumlcates on the rear hatch. It washes off easily. Anyone have any ideas what the cause of this is.

Ummm...dirt?

Either that or you've got some bad exhaust mixture outa the pipe?

Aerodynamics are the cause. Any vehicle with a flat rear (Bus, truck, SUV, van, etc) will have that problem.

Most people just rinse off the back every now and then. If it really bugs you, you can install a deflector to redirect the airflow and that should take care of "most" of it.