I'd save you the hassle. Re-installing the game won't fix or change the behavior of a slider. That's... just not how installations work.
Viable troubleshooting options:
- Check / play with all the audio sliders.
- Check your audio settings outside of the game. Try playing with settings like "volume normalization" (also called "loudness" by some manufacturers; my audio control panel calls it "loudness equalization"). Volume normalization will attempt to make all of your audio present itself at the same level, i.e., if there's a loud explosion or a booming voice, those things won't be much louder than the other sounds being produced. With volume normalization off, the dynamic range of the audio won't be limited. A loud voice heard after or during silence will be extremely loud. Along these lines, play with equalizer and "environment" settings (also called "virtualization," or "virtual surround"). Both of these can be set so that certain frequencies of sound - such as voices - are much louder than sounds around them. Some audio drivers even have a "karaoke" mode which can cut - or boost - voices. Make sure that's off.
I am not sure what other advice to offer. The only thing I can guarantee is that if you re-install the game, it's not going to change how sliders work.
Good luck tho!