Sounds are only present in content from the v0.35 update onwards. Earlier content does not have any.
What I mean is, there won't be any sound until you get to the content I added in v0.35. Just keep playing, and the sound will kick in once the storyline from the v0.35 update begins.
I honestly don't know how to express this clearly to every player. I've been asked this question ten times over the last few days. Do you have any suggestions for a notice or a tip?
I think what is most confusing is that I downloaded the v0.5 and played through it and then I got to the part where it was showing the side mission scenes selection but was not able to go further and there was still no sound. Honestly your explanation is very clear but unfortunately some of us are very slow, sorry.