So, preventing this behaviour involves only changing the car's input source back to whatever it was prior to connecting the USB cable. I can't comment on the RAV4 specifically, but in most vehicles the input source will change as soon as you plug the phone into the USB port. That's because the USB port on the RAV4 (along with many vehicles in recent years) is designed to be used for both audio playback and charging. Your phone isn't muting itself, it's doing exactly what it's supposed to do - trying to play music through the USB port.
