well it could be...
anything - did you do a good visual inspection for dry and worn out parts...

there are only a few spots with rubber -
the upper control arms, the swaybar (fun), the eccentric, the track mounts (guide rod), upper spring cup -

it could also be a shock tube if its turn sensitive
or a ball joint...when i first got my w123 and did basic overhaul i was shocked as to how destroyed the ball joints were because they shown no signs of wear...like much of the suspension.

steering -
might be the steering dampner, mine did not have one so i installed one, there are two to choose from a German one, and a Mexican one. could be the idler or a rag joint in the steering column...

so hard to say without being there to hear it...sorry
Jake