Hello. I am really happy to post the solution I found after over 100 hours of messing with the OS.
It seems that my motherboard's chipset ICH9 was not supported correctly by High Sierra drivers.
After installing the AHCIPortInjector.kext found here: https://www.osx86.ne...rtinjectorkext/
the sound problem got fixed completely.
I hope other people find this helpful for this or some other related problem.
Cheers!Go to the full post