iPod Touch (latest) plays audio through speaker, not car

Here's something weird. Attempted a search, but couldn't find it.

Got a new iPod Touch a few months ago. My typical routine is to load it up with podcasts and audiobooks and music, then plug it into USB (via the center console USB port).

Lately, in the last couple weeks, when I plug the device in, the device is recognized via iDrive (as usual), but audio plays through the device. No amount of unplugging or replugging, or turning the car off and on again seems to get it to play though the car's speakers -- except physically powercycling the iPod. Then, the first (and only the first) time I plug it back into the car, it will sync and play content out of the car speakers *once*. If I leave the device plugged in, and change nothing except turn the car off (even for just a couple seconds), the next time the car starts up, the device reverts to playing out of its own speakers. No amount of trickery or unique sequencing (that I have discovered) will convince it to play out of the car speakers -- nothing, except powercycling the iPod.

Has anyone experienced this before? Any ideas?