I had a similar sound on a 93 300E and it came from the rubber suspension bushings. A little WD40 sprayed on the bottom suspension bushings and it was good for another couple of months. Sometimes it sounded like the front end would fall out but really a nothing. Although I guess it could happen at other times, it did seem more pronounced when you were turning. Maybe you will be lucky and find it is a cheap, simple thing. No, I doubt that will happen if you have my luck!