It could be your upper control arm ball joint... grab it with your fingers and push the car up and down... if you feel a play, then you will need a new one.
Based on your description, it sounds like it might be a suspension bushing. I've had the same symptom with both of my 300Ds. It gets worse in cold weather when the rubber becomes less pliable.
I've tried shooting WD-40 into the bushings, since the garage I deal with did this once, but when I've tried it, it hasn't helped any.
Geoff
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