Have someone hold foot on brake w/engine at idle..this will cause the rattle while you take a long screwdriver or bar and insert it into the side of the top rubber bushing mount of the belt shock eyelet.. Twist the bar and see if the rattle ceases...very common and overlooked rattle fault on that chassis.
Easy fix is to sandwich an O ring between the damper eyelet and the mount to keep the bushing from rattling against the mount.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1993-Mercedes--benz-190e--.3-Cooling--System&yearid=1993%40%401993&makeid=63%40%40MERCEDES%2DBENZ%40%4063%40%40MERCEDES%2DBENZ%40%40X&modelid=6132%3AMBC%7C1485%3AED%7C10000009%3ASM%7C846%40%40190E+2%2E3&catid=240909%40%40Cooling+System&subcatid=241025@@Acc%2E+Belt+Tension+Damper&mode=PA

__________________
A Dalton