Just completed update Alpha [Dev] 0.51.103048. While in helicopter there is not sound effect for copters. Also moving to external view and there is also no sound effect for copter. I have other sound effects, such as weapons fire, and voice actors. I double checked the sound levels in game and the settings are all about 75% except for music which is off. Adjusted levels slightly higher and turned volume up on speaker and there is no helicopter sounds.