On most Mercedes from the early 70's up to the late 80's (including 114 115, 116, 107, 123, and 126 chassis cars) with independent rear suspension it is not uncommon to hear clunking noises under the back of the car while you are driving. Sometimes finding these clunking noises can literally drive you nuts. Do not just throw parts at the noise until you actually find the cause. There are a number of things that can cause clunking around the rear end while you are driving, but one of the most common is a worn ball socket in the one of the sway bar links that attaches to the outer hub on each side of the rear end. Upon a casual inspection you may not see the wear in these links and of course if it's under tension you may be able to feel it either.
Problem & Solution
Common among these chassis:
When these ball sockets start wearing you are going to hear clunking when the rear end moves up and down while the car is moving. The best solution to this problem is to simply replace both link assemblies. I recommend replacing both sides at the same time. They are an inexpensive part and are easy to replace with the car jacked up in the air and the tires removed.