Radio problems 2003 s500
Hard to say without checking out the headunit. What you describe is not a common problem. Could be a short or could be power transistor failure. Depending on your location there are auto radio shops which specialize in German or European cars. Those would be the best places to have it looked at. Avoid shops with HUGE bazooka style speakers in the window.

BTW, there is a Audio & Electronics forum here for questions such as this. This forum is for questions about site use. Not much traffic as you can see from the unanswered posts below.
Finally, both Becker and Alpine, the two most common suppliers of OE MB radios have repair/exchange services. I'm mostly familiar with Becker. You can pull the radio yourself and get an exchange or you can go thru a dealer. Beware anytime you disrupt the power to an MB radio you will need the radio's code to restart it after reapplying the power. Usually 5 digit code on a credit card sized card with OM. If you didn't get it, you can find out from the dealer with identity and proof of ownership.



