A while ago, every time I got into my car, my tunes would start playing with no way to turn them off.i had to delete every tune in my library. NOW THE MINUTE I START TGD CAR, MY MESSAGES START TO PLAY. WTF?
Check your car's head unit's settings and see if it isn't pulling media/messages automatically. Same thing on the phone (if you have Drive mode kicking in and set to read things out loud).