I had a similar case; 160k 300TE with a ticking noise at startup. I was certain that it was a lifter/cam follower. However, my noise wouldn't go away with RPMs, only time. And it would still occasionally start to tick while warm, at idle.

Thing was, the noise wasn't coming from the upper end of the motor, but rather over by the injector pump. I ran BG injection cleaner thru it (their "44K" product) and the tick's gone. I concluded that it must have been the pump, which has been quiet for the last 5k miles.

Just a thought...I'm inclined in your case to agree with my fellow respondents, but I wanted to apprise you of my out-of-the-ordinary problem & solution.

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Best regards, Michael
'92 500E
'88 300TE