During afterburn is someone is talking then it is so muffled and twittery that i can barely understand them. Otherwise sound is fine. I have a sound card and am using EAX 2.0 and hardware mixing.

Don't take this the wrong way, but have you tried turning up the "speech" and turning down the "effects" sounds to see if that helps??

Could be your audio drivers, speakers, limited audio channels in game engine, etc, etc...

If nothing works... I guess you could just turn off afterburning when someone is talking??