The noise is in my engine too. Happens at idle and when I rev the engine. Mostly at start up but then gets more quiet. Once I start driving I don't hear it as much. I noticed it on day one 5 years ago and mentioned it to the dealership. They said it was normal. So far 56K miles and no problems. It will continue to 200K miles with no problems. I think you will find this is normal and in most crossfires.... get used to the noisy Mercedes engine.

You can spend the time and money replacing every part of the engine. The noise will keep coming back. The only thing you gain is a potential problem from the dealership. Why waste the time and headache letting some moron touch your car.... just ignore the noise or enjoy the noise. Every time you hear it say "It is a Mercedes engine". Your car engine will outlast most of our lives I am a pretty **** guy and I DO NOT ignore problems. I just don't think this is a problem at all.

If you wanted a really quiet car you should have bought a Lexus I will keep my noisy Mercedes engine.