Jerrad at IPD pointed me to this solution, which solved my similar noise
problem recently on my 91 240:

There is a fastening nut, maybe called the glan nut or cap nut, midway up
the length of the strut assembly that can make a lot of noise over small and
medium bumps.  It's not unusual for this nut to loosen over time.  It holds
the shock absorber insert to the strut assembly.  To reach it, jack up this
corner tire (right front).  This will extend the shock and spring and give
you a workspace between the top of the tire and the wheel well opening.
Turn your steering wheel all the way to the right.  Reaching inside the
right suspension spring, lift the protective rubber sleeve a few inches to
reveal this cap nut.  You will only see the top lip of this nut, because its
threads are down inside of the strut assembly.  With a plumber's pipe
wrench, slide wrench through the spring to grip the slightly noched top edge
of the cap nut and tighten about the same torque as lug nuts (gut feel
method).  If this is loose more than 1/2 turn, it is probably the culprit.

Other suspects to test for include worn ball joints, worn bushings occuring
anywhere over 100,000 miles (average, but many owners last much longer).  A
little less likely is loose bolts/nuts on suspension/steering, but should
not be overlooked.  Also, it maybe the shock, but I'm less knowledgeable
about various brands of shocks and construction.

P.S. - Never forget to secure the jack with a proper lift tool.  If the car
slips from the flimsy jacking tool while you have your hands working with
the cap nut, goodbye fingers and hands.