Thread:Deathstalker666/@comment-26005008-20150619094203/@comment-1496755-20150620131227

From what I've read, all sound effects for Quake were done by Trent Reznor... gun shots, grunts, screams, etc. Maybe he used his own voice for the Enforcer too (after some "treatment", of course).

Besides, the Enforcer's speeches are treated by the game as monster sound effects, not as voiceovers (like the ones in Q2 and Q4 that can be heard at any time, serving some kind of purpose for the game plot).