I can't take any credit for this tip as I found it on macOSXhints. If you want to get better reception with your FM transmitter like an iTrip, then remove the external aerial from your car. It will now only pickup the signal from your iTrip. I tried it today and it was brilliant. My iPod is now great to listen to. Luckily I don't listen to FM radio stations so I don't miss the aerial.