My AM reception has always been bad. If yours has gotten noticably worse it may be the coaxial wire from the antenna. I believe the antenna is etched into the left rear quarter panel window (you can see it). Try checking the connection from the antenna to the radio. The Online WDS drawings at the top of the page may help. Search "open Online WDS" threads if you cannot read them. Good luck

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2013 X5 3.5i M Sport
2004 M3 cabriolet SMG