This, BTW, is a really interesting trick that Doom pulled. There's actually only a single death sound for each type of monster.* But for some monsters, the game plays it back at a random speed--also changing the frequency, like an audiotape on fast-forward--so it becomes a brief shriek, a drawn-out groan, or something in between. This gives an impressive variety of sounds without adding extra memory-heavy samples.
Hardly anyone was aware of this as far as I can tell, which is a testament to how well it worked. I only noticed it when playing a goofy little mod that turned zombie sergeants into Energizer bunnies and played the "still going" clip when you killed them. The effect is obvious when there's actual speech involved.
*Not counting the "splatter" sound when you gib any of the gibbable critters.