Halo Reach Firefight matchmaking: Elites make Halo 3 death noises?

The other day, I was playing matchmade Firefight games in Reach, primarily to get warthog kills for the Beast Mode challenge. I killed some Elites, but they made Halo 3 death screams, even though I was playing Reach. It happens with almost every elite that dies in matchmade Firefight games. Does anybody know why this happens, and if it’s intentional or not? I can’t be the only one who hears this. By the way, this does not happen in Custom firefight games.