Sound mods created for version 1.38 or older might break due to FMOD structural changes in 1.39. Verify that your sound packs explicitly state 1.39 compatibility. To help find relevant files for your setup, please tell me:
A dedicated turbo slider was added, allowing for more immersive engine noise tuning. download ets2 1.39
Do not load a modern version 1.50+ save profile into version 1.39. It will corrupt your save data. Always create a fresh profile specifically for your 1.39 trucking career. Sound mods created for version 1