A video of this occurring: http://www.youtube.com/watch?v=FE5pp5xzE_E&feature=youtu.be
Other players have reported the issue on the BIS forums:
http://forums.bistudio.com/showthread.php?157247-Sourround-sound-problems-DEVs-take-notice
http://forums.bistudio.com/showthread.php?147828-5-1-Surround-sound-not-working
This is occurring on surround headset/speakers. Starting the game with this headset unplugged and using a normal set of headphones plugged into the headphones jack, this issue disappears. Issue has been reported by other players on the BIS forums using different hardware configurations.