I made a post at least a year ago about this same topic and a BI employee told me they knew about it and where working on it but since then nothing, so here it is again.
with certain computers, arma 3 when on 64-bit mode will have issues with audio when in first person within vehicles and buildings. this causes VERY loud cracking noises and large FPS drops. I have experienced going from 60 FPS to having to shutdown my PC because the game is that laggy and will not respond to imput. PLEASE if fix this.