when i hooked my laptop up to my tv using an hdmi cable the sound was totally crappy. i read (i cant remember where, sorry) that to fix it you need to disable the normal audio interface:
System > Preferences > Sound > Hardware
choose Internal Audio
it worked perfectly. when i was does and renabled Internal Audio, i couldnt hear any sound with normal audio, like youtube in chrome or playing local files with vlc. to fix this i read No sound at all.
all i had to do was this:
rm -r ~/.pulse ~/.pulse-cookie