I have a Pixel 4, most of the time when I play Pandora, i turn off my car the music stops and it's fine. However, a couple times a week at least, the music starts playing immediately on my phone after I turn off my car and it's quite loud.
@ouroboros2013 I recommend running through the following troubleshooting steps: Troubleshooting for Android Devices
Let me know how it goes.
Let's share music in the Music + Podcasts