Would love a proper fix for this as well. My solution was to delete Apple Music and all audio files on the phone. We always laugh when my wife's phone plays some Foo Fighters mp3 every time she plugs in, but it's super annoying. The breaking point for me was when it burned my entire monthly data plan streaming Apple Music. The car's speakers were playing the radio, so we didn't even know it was happening.

Doesn't happen in my car (Hyundai) over Bluetooth, only USB.