Becareful when you say "anything mysterious".
If the mechanic isn't trustworthy he will find mysterious things.
I own a 1986 300E (192k mis.) and it to will make this tapping noise when first started cold. It does go away immediately, had it checked out and it was the lifters, not lubricated well when started cold.
[This message has been edited by rich30769 (edited 09-06-2000).]