Dan:

Sounds just like the noise I was having with my 1999 C230 K. It was in fact the supercharger. I replaced it myself for $655 all parts included and three hours labor. I had it verified in advance that it was for sure the compressor. All you have to do is remove the supercharger belt and run the engine without it and if you don't hear the sound, then there you go. The belt does turn anything else. When I got my S/C out, it was clear that the bearings inside the unit were on their way out. Good luck.

JB