BMW I think used to code the head unit to the specific vehicle with the various modules. It prevented someone stealing the head unit and putting it another car. Then the only people back then that could code the vehicle was bmw and they would find out. Sounds like the coding of your head unit. That is what I am thinking about mine. My issue with the radio now is that when the car starts up all the speakers on both sides work fine then a short time later only the left side works. When the right side works at start up it is clear and crisp. New amp and tested with new radio module. I am now leaning towards the coding issue.

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2005 X5 4.4i M Sport
2003 X5 4.4i