Sirius Satellite Radio Cutting In and Out

[tjcin1]

This past weekend I installed the factory BMW Sirius kit in my 06 X5. In the driveway it works great, but when driving it cuts in and out badly. I feel the issue is probably with the antenna or it's mounting location. I installed it in the spoiler. Has anyone else installed theirs in the spoiler? If I have to install it on the spoiler, where can I get one that the wire exits the bottom of the antenna and not the side? I don't mind looking at the antenna, but I don't want the wire exposed. Any input will be greatly appreciated. Thanks, Tim C