Certain window tints can effect reception. When I had all my glass tinted, I was told that metal based films can harm radio reception when fitted to the rear screens of cars like the e34's ( glass with ariels fitted within the glass). Supposedly, the cheap tints that turns purple are the ones that you fit to the rear screen to not effect reception.
I had the more expensive film added to the rear screen, and experienced only a slight loss in reception.