if it is not associated with gear shifting / acceleration, this sort of clunking is caused by the sway bar links in the w124. see if you can induce it by swerving from side to side in an empty parking lot. that's how i decided that mine were shot even though they looked ok and didn't budge when they were checked up on a lift.
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"