Ok, so im having some complications with our Mercedes. I think that the car needs a new catalytic converter b/c it is making those rattling noise around 1000rpm. We hear it when we are in the parking lot just looking for a spot and sometimes, even at idle, you can hear it. Its like a scrathy, marbles in a can noise...what is it??? And when we are accelerating, it is like a bicycle chain noise. It's loud and sounds un-Mercedes like. What is it all? Theres also a rough idle...what is it??? Dont tell me to go to the dealer! i dont like them! Thanks!!!