Hi, I'm having this problem too. I've tried two sets of headphones and in both cases I can just hear a whisper of the speech as though it's in the far distance. The rest of the sound is absolutely fine.
I have also plugged speakers in, using the same socket (the only sound out socket I have) and the speakers are fine. This is really strange. And very annoying. I need headphones because I have insomnia and on those nights that I can't sleep at all I need to be able to watch telly (on computer) without waking my partner. Stressed!
Oh, also, I'm Ubuntu, and I had no problems until 2 days ago.