Within the last week, a gray-silver soot collects at the front of the dishwater; the soot collects near the hinge mechanism for the door... No collection is found on the items being cleaned... The soot is smooth to touch and behaves somewhat like grease when it is wiped away (smealy)... What is the "gray" or "silver" soot and how do we stop it from collecting??? obvioulsy, something is wrong with the unit...