That is a common symptom in cars with DSP where the amp is not coded to match the car. Are you certain that you do not have the DSP option? What is the year and model of your car? Is the setup original to the car, or is it a retrofit? Have any of the navigation or audio parts been recently replaced?

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2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input