The problem is the difference in level between different sources, combined with the car starting to play music from a different source when you start it up agai

The problem is the difference in level between different sources, combined with the car starting to play music from a different source when you start it up again. I have my phone playing music over Bluetooth at a normal volume (pretty quiet, in fact), and then I leave my car, come back and start it and some random local radio station starts playing at an ear-splitting volume.