Oh yeah this Issue... I am afraid there is no fix for this. I am sorry.
This Game was abandoned by the Devs years ago.
First the Game Audio is always way too low at Boot. So you have to higher the Soundvalue by pressing Escape everytime you relaunch the Game.
Than the Soundmixing especially later is not good at all.
If you have the Sound value too high every Sound can get corrupted.
The only Way you can sort of do something about it is play at the lowest Audiolevel through the entire Demo and than fix the Sound in Post.
The 0.8 Build of RE77 has better Audiomixing, still not perfect mind you but it is better than the 0.9 Build.
Once again I am sorry that I am unable to help you here!!!