found it, still no answer but John is on the problem, this problem has been around for awhile. I am thinking a NW pulley saver kit, and an NSK bearing should do the trick.

From Jerk to Chirp, the saga... - Page 2 - MBWorld.org Forums

unplug the supercharger clutch drive around see if the noise goes away. If it does you have your clutch engaging answer. Mine does not do it all the time so i have no way of really checking. Yours sounds pretty often I would think this would work for you.