It's called Retained Accessory Power (RAP) and the owners manual doesn't state anything about it being programmable. It looks like your only option is to open the door or turn the radio off at shutdown.

 

I don't know if this will work or not but, try turning off the sound effect that plays when the car shuts down. I'm thinking that the sound system is switching from radio to effects then switching back to radio at shut down. I'd try it myself but I don't feel like digging into the menus right now.

 

Semi-related issue ... I almost exclusively listen to either Pandora or NPR One via bluetooth from my iPhone. I've noticed that I will have issues with the connection the next time I get in the car if I open the door before I let the bluetooth audio source start playing again after turning off the car. In addition, if I open the door at the "wrong" time, the audio source will start playing from the phone's speakers a minute or so after I leave the car.

If I wait for the audio source to start playing before opening the car door, everything is fine. It may be related to my phone, but there is something fishy about the resumption of sound and the BT connection.

 

My ELR works this way. I usually am just streaming from Spotify. When I turn the car off the music stops (pun intended) and then starts up again until I open the door. It's kinda annoying. My solution is to open the door immediately after turning the car off.

What's weird is that music is about the only thing whose settings are remembered. When I get back into the car and turn it on, the music goes back maybe ten seconds and starts again. Things like whether I was in Sport or Mountain or Hold just get reset to the defaults.

 

I'm not sure if you dislike the pause in the audio or the fact that it doesn't turn off until you open the door. If you dislike the pause, disable the audio cues and there will be no interruption in the audio. See this thread for more info:
http://gm-volt.com/forum/showthread.../showthread.php?250937-Music-stops-when-car-is-turned-off&p=3519058#post3519058

 

I always have a habit of muting the sound before I park the car. So the fact it comes back on (but still muted) doesn't bother me.

 

All my audio comes from Android Auto (either Pandora, Audible, or Spotify, usually), and when I turn the car on, it is silent until I manually turn something on. I'm not sure if there's any sort of similar behavior without using Android Auto, but if you have an Android phone, one solution would be to connect it and start an app playing audio before you turn off the car. A bit involved if you don't normally use AA, though.

 

I have very few dislikes about my Volt, but this is one of them! Give us an on/off choice, GM!