When you are in a Car or Helicopter , even if it has open windows/doors like in the little bird or even the open ATV , there is no envoirnement sound.
- Legacy ID
Get into a CAR/Littlebird/ATV and stay on ground , get into First Person
I noticed this when it was raining. Sat on an ATV and the rain sounds stopped. The game engine assumes all vehicles have a roof I think... In my experience the environmental sounds didn't start again after a while, but didn't double check that.
If you go into 3rd person view of course the sounds do start again.