I had the same thing with my 300sd when I bought it. Its a horrible punding in the front end. Since I have replaced the tie rods and wheel bearings up front. It is mostly gone, but every once in a while, I'll get it on certain road surfaces. I'f pretty sure its either slop in the ball joint, or in the control arm bushing. I've had the tires balanced, rotated and done several allignments, all at different places with no change.
