on Mercedes shop for analysis...

Unlikely, since the glow plug is inside the precombustion chamber. And, as we all know, there are only 7 tiny holes leading from it to the cylinder.

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Never a dull moment at Berry Hill Farm.

I just posted a reply for sound from engine compartment.

I would check 2 areas

1) the bottom pulley that is attached to the crankshaft. There r 6 bolts there. They r know sometimes to come loose or even break. Look at that from under the radiator area.

2) Could ur vacuum pump be coming apart? Check and see if u can isolate the problem.