I just repaired my C36 from the "whirring" sound. A vacuum hose had rubbed against the inside sharp edge of the door panel and split the vacuum line in half. I used a shrink tube to fuse the 2 plastic lines back together and split a small piece of vacuum tubing down the middle and wrapped it around the vacuum line to keep it straight and from rubbing on the sharp edge again. Power locks work fine now.

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