The menu point ""Update in background" has 3 settings: None, Graphics only, Graphics and sound.
This setting corresponds to "pauseMode=" in the user_settings.DayZprofile file, witth None = 0, Graphics only = 1, Graphics and sound = 2.
Changing this setting to "Graphics and sound" while ingame works correctly and sets it to 2 in the file.
However when you restart the game it's back to "Graphics only" instead, which would correspond to 1 in the file, even tho it's set to 2.
Therefore you have to change this setting manually everytime you restart the game.
It's a fairly important setting and not just for convenience, as it allows alt-tabbing the game and still hearing what is going on. It's basically a must have for anyone playing fullscreen. I strongly suggest that "Graphics and sound" be the default setting, too.