First, forgive me if I'm so late asking this. It's just that I haven't tried to figure it out so far.

1. Somewhere in Alpha Labs, forgot which level, probably 1, 2 or whichever. It's the level where you go through a crawlhole with two exits, the second one being optional. During one of your crawls below a grate, you hear someone doing a chant or spell in an unintelligible speech. I'd say it's kinda odd, because the zombies and monsters you'd encounter in Alpha aren't intelligent enough to utter stuff. I'd really love to know who could have said that, and if there are/were blueprints/expansions detailing that aspect.

2. There's a stock background laugh that isn't Betruger's voice, neither Sarge's, Guardian's nor Cyberdemon's. It's a slightly lower pitched Hehehehahaha that plays at random moments within the game. Whose voice is that?

1 and 2 - think about some kind of evil being, devil, or other demon, maybe satan. D3 is not only about killing monsters and zombies, it is about fighting evil and evil know how to do all sorts of scary tricks.