I've looked and can't seem to find an addon for this. The sounds our toons make while in battle is just so annoying. I'm talking about the grunts, HeeeYa's, etc. Lol.
We are not able to mute them or any particular sounds. One could only mute the total combat or other total sounds.
As there is no way to determine "when the char is grunting" by API or chat output there is currently no way I'd know of how to do this, sorry.
Write /bug ingame and tell others to do so, use the official forums and ask for a setting please!