[superfret78]

I'm not up to date on all Mercedes or for that matter..any newer car electronics but the check engine light usually flashes when the computer throws out a trouble code indicating a problem with one or more sensors. You might want to have that checked by someone who has a code reader. Regarding your catalytic converter...well if it is a problem internally with your cat. converter and you want to take it off and replace it with straight pipe it won't hurt your car any. In fact your car should have more power due to the reduced exhaust backpressure resulting from removal of the cat. converter. Just make sure it really is legal in your country. The only down side of not having a cat. converter on is that you increase the amount of harmful emissions your car releases..if you're concerned with environmental issues you may want to factor that into your decision. Now let me say this....before you agree to having a straight pipe put in, make sure that the rattle is not caused by loose exhaust hangers. Sometimes things can rattle if they're loose. Also, most cat. convertres have a heat shield on top of them, as they get extremely hot and run up close to the underbelly of the car. Often times the heat shield can come partially loose and rattle as well.