I know the rule of thumb about the quality through the fm transmitter on either Sirius or XM, (especially in bigger cities). Last weekend, I traveled to Chicago from West Michigan, and before I left town I took my vehicle through a car wash. I always take off my car antenna before I go through so it does not get bent or come off and do damage to the car in the wash. After I did this I got better reception on all the frequencies through the FM transmitter on my XM roady 2. I also did not have to change the station or have any interference when I was in Chicago which is a real shocker because Chicago has a radio station on seemingly every other frequency. Anyway, I left the antenna off of my car so that I can continue to enjoy the crystal clear reception I now get on the FM transmitter, and wanted to pass this info along to others if they wish to try it.