I know that the FM antenna is in the driver's side rear window, but if I change the roof antenna it affects the FM reception. I can't explain it.

I've tried three stubbies and the original/stock antenna. The stock antenna gives me the best reception, but I'd like to improve on that because the stations I listen to during my long commute are not very strong.

I don't know if it makes any difference, but I have the HD radio and the HiFi system.

I've checked the NAM vendors and a few others, but haven't found anything. Any suggestions?