I recently purchased a 2011 S63 with about 13K miles on it, certified pre-owned at a local MB dealer.

I have a knocking noise that is quite audible, at idle. It sounds like it's coming from the front of the engine. I've already taken it to a dealer twice now. The first time they replaced timing chain tensioners, didn't fix it. The 2nd time, we all stood around listening to the noise together, before I dropped it off again. But next day the called and said it's "normal" and to come and pick it up.

I just took it to a different dealer, after first interviewing the AMG mechanic who would be working on my car. He's a little young, but seems passionate about his job and these engines. He was honest and said he didn't know what that noise was and would have to spend some time with it. He also said that he'd like to put it next to another car with the same engine and compare them. He also said that, sometimes if a dealer cannot diagnose a problem, they can call in someone from corporate to help. Sounds cool, if they are willing to be relentless like that and get it resolved for me.

Has anyone else ever encountered this? What do you think it is? When I have the car running in the garage, if my wife happens to walk out, she says "what the hell is that?" and then proceeds to make fun of me for spending this much money on a car that sounds like such a cheap piece of ****.

Thanks for reading and I hope someone has some input.