Hello. Just to update this scenario:

The car is at the dealer. One of the mechanics, the SA, my friend, and I all witnessed the noise at the dealership "check in" bay when I started the car up two hours after I dropped it off this morning. The mechanic at first said the noise was somewhat normal (hesitant). He then said it sounded more like a timing chain issue. I hinted at the fact that my research indicated it could be crank bearings, and MB is aware of this issue on the M272 motor.

It wasn't until I showed him an invoice of an anonymous person on the internet that had this same issue fixed that he said "I guess it could be that, but we have never done one".

Long story short, it went from being "normal" to "a problem", to getting shop foreman/MB involved. They wanted to keep the car there for 2+ days for investigating so I left it with them today. Will see what they come back with. I hope good news. I really want to get this motor repaired as I plan on keeping this car till the wheels fall off, and quite honestly, its embarrassing trying to explain a loud, consistent (sitting for 30+ minutes hot) engine knock to friends and family. I truly believe this will effect the longevity of it (I hope im wrong).

I will let you know what they come back with.

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K