I had this too, then it got really bad, all the time. I thought for sure it was the front, but had my stalwart co-tech (wife) stand outside while I slowly drove by the house. It was the rear. Wheel bearing and Hub need replacement. Brakes and E-Brake shoes got done too at the same time as they were shot. This on the ‘86 300E with157k.
1986 300E Anthracite + ECodes + MB Mileage Award