I have a 560SL that is making a strange noise whenever one changes
directions, either forward to reverse or reverse to forward and
applies the brakes.  The noise is a loud clunk and almost makes you
think you've hit something.  If you keep moving in the same direction
and apply the brakes again, there is no noise.  Therefore, it is as
though something is shifting positions as a result of the application
of the brake with opposite wheel rotations.  Most of the front-end
parts of this car have been replaced, so its hard to figure what might
be the cause.  Has anyone seen this sort of problem before?  Any
suggestions on where to look?