One of the stations I listen to often does not come in very well but if I turn the truck off its perfect. Don't have this problem with all stations though.

 

There is so much energy in the ignition systems in these new vehicles, I would be willing to bet that the radios have active filtering that is clipping the ignition noise as well as attenuating some of the sound that you normally hear when the engine is not running..

Regards - Randy