Marc, can you provide more info on the specific antenna that you purchased from Amazon? Thanks!I had exactly the same issue. No fix from BMW. In fact, they initially thought it was a "faulty" antenna and replaced it. No change or improvement. Ultimately, I was told the issue is interference from the metal windshield support. I bought a $20 dollar antenna on Amazon, and attached it to my top box. XM works flawlessly now!