TL;DR: Tweaked sound file (n_metal_plate_2.ogg) to remove footstep sound crackle when walking on metal surfaces. (Works for both PC and NPC, as they use same file)
Full: Finally got around to playing CoP after enjoying previous games a lot, however I've been having very annoying constant crackle when walking around and I couldn't find out what was causing it, after a lot of time searching on google, changing all sort of settings, and trying to narrow it down when exactly it happens, I've realized it's not engine/system issue, but actual footstep sound file simply had that crackle in it... I've edited it out of the file, and there it is, no more crackle.
Hopefully this will be useful to others annoyed by this kind of stuff.
Nice job, always nice to have little fixes like this.