As I was playing, the audio suddenly cut out almost completely. (Weirdly, the sound effect for opening boxes and taking loot still worked). 
 

I'm sorry for the late reply. To expedite your issue, if haven't done so already, we ask that you please visit http://privatedivision.com/support and report the issue there. This will get your issue into our publisher's queue to ensure the fastest possible turn around time. Again, I apologize for the late reply and thank you for your patience.

Are you alt-tabbing out of the game at all? That will sometimes cause audio issues in games. Restarting the game should resolve it.