I had a couple of lifters tapping, so I took it to my Chrysler dealer. They checked it out and said that the lifters needed to be replaced.
They replaced them on my '05 Roadster under warranty. No more ticking since they changed them out.
Has anyone else had the same problem? I have owned a lot of cars, but have never had to replace the lifters.

 

It seems a noisy valvetrain is a somewhat common problem with this family of MB motors. Mine had a nasty tick when cold until warmed up from abnout 10,000 - 18,000 miles and then disappeared all of a sudden and hasn't been back.