I am finishing up an aftermarket install then I came across this thread. I don't listen to radio much now that I've gotten a taste of satellite radio. I decided to try the radio just to see what it sounds like. I tried it in my garage with the garage door closed. As expected there was a lot of static. When I pulled the X out of the garage it sounded a little better but not as good as the factory system. After giving it some thought I realized that my X (2004 4.4i) has that diversity antenna amp. So I jumped the power antenna feed from the aftermarket radio to pin 13 on the radio harness (I have an MID no NAV). According to the online WDS pin 13 is the "Antenna amplifier Diversity" connection. What a difference it makes! Even in the garage with the door closed there is no static.

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[Sold] 2004 X5 4.4i - Sterling Gray - Truffle Brown, Sport, Preminum, Rear Climate, DSP, Sirius, PDC, 132's (19 inch wheel), Comfort Seats
Dynavin, JL Audio Stealthbox, Alpine PDX-5 Amp