recently purchased a 2001 slk320 with 29K miles. Car has been fine, but about 2 months after purchased I noticed a strange rattling/pinging noise coming from the engine when I accelerate at start-up. I am not sure if it is coming from the engine or the exhaust. If I have the car in park and hit the accelerator, the noise is most noticable after I let up on the accelerator and let the car go back to idle. It sounds like metal rattling on metal. I am a novice when it comes to servicing my MB, so please be gentle.