I dont think it is a bearing at all.... I have the same problem at really low rpm take off almost like a high pitched chirp when your not getting on it. It is the clutch on the supercharger there have been numerous post about this on MB world I just cant seem to find them. Guys were freaking out taking there cars in and mercedes was replacing the whole supercharger because there was no way to order just the clutch assembly. With that being said when they got tired of replacing superchargers they started lubing the clutch. I will keep looking YTD i think there is no fix, but it wasnt as major as everyone thought.

Rudy chime in do you remember this?