No sound but in very specific parts of the game....

[Papa Emeritus IV]

So I just installed the game, verified file integrity twice and the first thing that caught me off guard was that there was no sound in the opening cutscene, but i got to the landing screen and there was sound, no problem, okay weird maybe my headset was off, i turned it on and off just as i got to the landing screen. So I start up campaign, classic, its all good until I hit the cinematic right before the first mission, again, no audio. I couldnt find any other issues online that dealt with this specifically, fiddling with binkw32.dll stopped the game from launching so i restored it, had a poke around in the files to see if the cutscene file were missing the audio, but no, i was able to play them through vlc player no problem, and the audio was there, weird. I did notice that the voiceover audio was absent, probably stored in a separate sound file thats meant to be played over the cutscene simultaneously, but yea, its not all cutscenes, the ones that were giving me trouble were:
cuba_load.bik
number_lady_intro.bik
treyarch.bik

Again, the audios fine when played on vlc player, but in-game theres no audio, and no voiceover. Any thoughts? anyone know what files script and trigger the .bik and audio files to play?

[PsyHaIceFire]

There could be two problems:
First, a driver issue:
You mentioned you are using a headset, if you are using it via USB check if there is a driver available.
If you are using it via 3.5 audio jack or any other audio plug, search for the latest mainboard audio driver, or soundcard driver.
Even if it doesn't fixes the issue, updates are never a bad idea.

Second, a file issue.
Audio files are stored in those .iwd files in your main folder.
Maybe delete all of them and click verify game files.
That should give you fresh new .iwd files.
If that doesn't fixes the issue, ask a friend if they could give you their .iwd files.