New noise

[TonyFromWestOz]

I adjusted the valves on my '84 300D 6 weeks ago and everything seemed fine.
On Saturday, I went for a 250 km drive in the country, cruising at up to 145 km/h (somewhat over the 100 limit) Fatmobile III purred like a kitten, although somewhat rowdy kitten at that speed with the sunroof open.

Today I note that she has developed what I thought to be a tappet rattle (OK Cam follower noise). Sounds like a tic tic tic at the motor speed. While driving up the last km to home (up steep hill) the noise got noticable louder. It became a TIC TIC TIC, still at the same rate.
I thought that perhaps I had a loose valve adjuster nut, so tonight I pulled off the cam cover and checked the valve clearances. all OK.
After restarting the engine, the noise is still there, but after a few minutes of idling, a new, rattling noise started. I shutdown the negine. I restarted the engine after checking for obvious external problems without success. The TIC is still there, as loud as before, but I haven't heard the rattle again.

Can anyone shed some light?
The car has a genuine 286 000 km on the clock & burns negligible oil. There is no smoke at startup or at full power.