I have an 01 CLS with 22,900 miles and I've been hearing a rattle while driving quite similiar to that of my old 88 legend with 244,000 miles. Most recent occurence was last night I was driving about 50 mph and started to accelerate softly and the sound occurred again. I think it's lifter noise but I'm no tech.

 

I'm at 28k and once and awhile i hear the same thing. I'm gonna have them check it at 30k.

 

If you have Comptech headers check for a small crack in the welding by the heads. I have replace my headers a couple of times and it was due to the leak. Sounded like a ticking sound from the values or something at low RPMs during acceleration