Sometimes. Usually worst at idle and mid-range speeds, depending on when the chain resonates.

Easy to find it -- it will be located at the very front of the engine and won't go away as you loosen the injector lines one at a time. If it goes away when you loosen an injector line cap nut, it's a bad injector (or cylinder problem).

Other things can knock, too, though -- rods, main bearings, bad alternators, loose AC compressors or brackets, etc.

Rods and mains will have a distinct clank to them, definitely metal to metal noise. Injector knock is often referred to as "nailing" because it mimics the sound of a 16 oz framing hammer driving a large nail into a heavy oak timber -- definitely a snap and not like a metal to metal impact.

injector knock will be definitely in the head -- rod knock lower down, (ditto for wrist pin noises, sometimes called piston slap, although that's different and I've never heard it in a Benz), and mains will be definitely at crank level.

Alternator stator/rotor noises are similar to injector knock, and the belt will wear very quickly (I know, the one on the 220D did this).

Last, missing rubber bushes on a York AC mount, or a loose or missing mount bolt, will make a sound VERY similar to a rod knock, and you will have to look closesly to see the mount move!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!