Their appears to be a wide spread problem of a lack of understanding on how to change a belt on a Mercedes Benz or more specifically how to release the belt tension. Usually people resort to crowbars and inflict damage as was the case when I bought my ML320 used. When the pulleys become dented or damaged then they must be replaced or they will ruin the belt. Squeeking is a sign of damage.
Here you'll find a picture of the tire tool properly affixed on the belt tensioner release nut. That's right. All it takes to change a belt on a Mercedes is a new belt and the tire tool. The tire tool fits right on the nut probably by design and all you have to do is lift and release the tension. Also their is a hole for a pin to hold it open but it is beneath the pulley and viewable from the underside.
