Hello, I'm suffering from a bug that doesn't sound all the time. What I tried to do to fix this bug is to set up the speaker as a stereo, update the sound driver, reinstall the game. But nothing happens. How can I fix it?

Did you install Windows update recently?
Things you can try:
-Change audio sampling rate
-Disconnect each audio related device, except the one that you're going to use.
-Make sure the default output is the correct one at Windows audio settings (disable the rest, including digital output)
-If your audio driver becomes with an application take a look.
-Disable the HDMI audio output.
-Look at volume mixer
-Make sure "Spatial audio" at Speakers/Hadphones properties (Windows) is turned off
-Verify Integrity of Game Files through GOG client
-Try to change between 5.1, stereo and 7.1 and look if something changes

Hope it helps. Cheers