Did the mech who put on the brakes apply some ant squel compound to the shim? If not, try that and make sure the shim is on right.

Also are you using a resurfaced rotor or new rotor?

From what I hear, MB rotors SHOULD not be resurfaced.

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1997 Silver AMG C36
OEM Advantegarde Grille
OEM Clear Corners
W210 Blinking mirrors
Eibach/Bilstein Combo
Zender Rear Lip Spoiler