You have a bad antenna or a broken antenna cable. Double-check the antenna connection on the back of the MKIV. If that looks OK, then you will probably need to buy a cable or antenna. I would buy the antenna cable first, since that is cheaper and you can directly run it to the antenna. If that does not fix it, then buy a new antenna.

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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