Update: mystery (somewhat) solved!

My 70+ year old dad put one in the car. I would have been less surprised if I was stalked rather than if he knew what an AirTag was. Apparently it was a gift to him. However, a few things still don’t add up:

1. I drove to Michigan a few days before with that car (alone) and never got a notification. I also drove around Michigan for a few days and never received that notification.
2. The AirTag was not popping up on any bluetooth device tracker
3. I appreciate the comments stating that the speaker is easily removable, however my dad is not savvy enough for that. I still don’t understand why when I clicked “play sound” when in/around the car, nothing happened.

Thanks for all the help and concerns. Was getting a bit worried there!