After several times of making horrible static and getting all better, my radio is now silent. Radio itself is working, but no sound. Dealer diagnosed it to be a bad amplifier, so I purchased an amp with same part number as old one - from a dealer in used MB parts - Adsit. My husband plugged the new amp in and still no sound. Radio has correct code. Any suggestions out there? Is it a fiber optics problem - do I need to go pay the dealer his high labor costs? Any alternatives to that?