Hmmm, now how can it be rusting up in there?!?

The rust comes from a major design flaw, that's how!

The handle space to lift the rear hatch is rusting out from water collecting inside the door. It has already shorted out the right hand side license plate light. This spot is not normally visible nor exposed to the elements (the hatch door is up in this photo). The rust is caused entirely by  Mercedes design flaw in the ML series and this flaw goes back to 1998 and has not been corrected: I have the same issue with our newest ML although it hasn't started rusting yet, there is water appearing.