Clicking Valves on 1990 300TE

[Barn]

1990 300TE 4Matic with about 180,000 miles. The valves click until oil pressure comes up, but then go quiet for a period of time. Then one or more valves start to tick. It will come and go but is definitely getting worse. In the mornings I can hear them click when driving for about 2/10ths of a mile before stopping. They often click when warm and idling, but once again the clicking will come and go without a change in RPM or oil pressure.

Any ideas? Could it be something other than the valves?

Thanks.