I had a barely audible sound issue this week. At first I thought there was no sound, however going to the audio options menu and cranking the volumne I could barely here the setup sound gun fire. I tried re-installing ARMA2OA/DayZ/Betas a couple times but every time I installed the latest beta, the issue would come back. I eventually upgraded my audio drivers to the latest version and the problem went away. Give that a try.