I've noticed this too with the 15 I just picked up on Sunday. Some times at 70 the radio is clear as day and then it will get quiet and louder. Don't really understand. Don't see how it could be an antenna problem or the radio just not picking up the station. This was never an issue on my 2010. Hope someone has an answer! Also does yours do it while listening to music via usb or bluetooth? I haven't tried that yet.