This is what happened when I moved my antenna under the spoiler. Not quite as bad as you describe for me though. But every time we drive in the mountains now that radio goes out (it did not before in the same areas). Maybe position it differently in the spoiler? I have not tried that myself yet. Mine is positioned directly in the center (near the screw) and just double sided taped right where there is a few inches of room. Good luck! Let us know if you find a fix or not!