Pentakill Karthus taunts muted

I pretty much bought pentakill karthus cause of the taunt animations, also I frequently play the champ itself. I had no problem using the taunts, but eventually I couldn't hear them anymore. I have also asked my friends if they could hear the taunts unfortunately they couldn't hear them as well. Please fix this :( I know its not my computer cause I can perfectly hear every other champ I use.