PS3 sound problems

I have noticed recently whilst playing my PS3 that there are some sound issues with it even when my tv volume is full. I have not noticed before but i have realised that when playing blu ray dvds that you cannot hear the voices of the people in the movie. I have also noticed this on the game assassins creed 2. I have checked my cables are secure and tried swapping hdmi cables. You can hear the sound fx e.g. explosions but absolutely no voices, is there anything i can do to fix my ps3 without sending it off

If you have any ideas email me at intoxicatur@hotmail.com