177k miles OM651 Mercedes diesel engine, not sure when was the last time the fuel filter was changed, can the rattling noise be the fuel filter not giving the engine enough fuel? :
Mercedes-Benz OM651 engine
Mercedes-Benz introducing new diesel family in E 220 d this spring; new OM 654 with 13% lower fuel consumption; diesel “indispensable” - Green Car Congress
MERCEDES-BENZ OM 651 SERVICE MANUAL Pdf Download | ManualsLib