MAJOR LEAGUE STONERS

Made a quick video of what the machine guns sound like to me. It just started happening.
It only happens on Single Player maps on Multiplayer.
Any idea why?
https://youtu.be/4eZ6-ogYcDw

If its on the custom maps only, I believe there is a sound issue within the game itself. I see that on the logs quite a bit. Brave may be able to shed more light on this.