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 engines - Mercedes OM 651 engine (2008-)
ENGINE CYLINDER HEAD R651 016 R651016 MERCEDES-BENZ DAIMLER OM651 OM65 – Topmotors.lt various engine parts crankshaft cylinder head piston rod block sump oil pump camshaft rocker lifter cover chain adjuster gasket bearings
New Mercedes-Benz OM651 twin turbodiesel - paultan.org