Mine tapped when I started it for about 2 minutes when it got about 12k on it. When it got to about 15k it stopped and is quiet at start up again. I think I thrashed on it a little bit the night before it started being quiet again. I think my car has a mind of its own because one day I was really serious and searched endlessly on the internet about this problem for hours. The same evening I went out to start it and voila! It was quiet and has been ever since for a couple weeks.

About the faint ticking at all engine speeds, I found a few people that I believe had m112 engines, but I forget what car, and they said they had the lifters replaced over and over and it didn't solve it and then their MB dealer had installed some kind of bushing in one of the motor mounts that cured the problem. It sounds like that may not even be a valve problem, but some sort of weird NVH problem