Your old radio probably fully muted when nav instructions came over. The Nav-Min function on the new radio adjusts how much the radio mutes with nav instructions. It is kind of nice, because you can set it so that it does not fully interrupt the music.

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SOLD
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