As a stopgap measure, until sound gets fixed

[Ataros]

Some people loose sound on Repka3 too.

Try switching forest completely off. 3-5 people reported it helps.
Try setting sound to ambisonic(iirc?) uncoded.
Try reducing texture quality and then other graphic settings.

There was a report saying switching from a gtx280 to a gtx580 fixed sound issue.

I guess sound files and textures are struggling for PC resources and textures have higher priority set in code.