One of the best tips I got off this forum was to tune the radio to XM Channel 1 (or is it 0?). There's nothing broadcast on that channel so it doesn't matter that the radio turns on automatically (or how loud you left the volume). This works very well for me because I only use Apple CarPlay to listen to music. I don't listen to any radio stations. Maybe this tip will be helpful for others too so I'm passing it on. 👍