Windows 7: Youtube Sound Distortion

Win 7 64 bit utilizing on board sound and IE 9.

This problem is driving me nuts.

If I playback my MP3/4 or DVDs through my speakers or headphones via my PC everything is fine, sounds are great, DVD play fine.

The problem arises when I attempt to watch anything on You-Tube.

Again videos play fine, no pixalating or buffering issues of any kind, it's the sound, it/s so distorted, so tinny when listening to music or anything else for that matter.

I have installed and reinstalled Flash, ( latest ), I removed Flash all together and installed an earlier version of Flash, no improvement.

I have followed several suggestion on this issue via Goggle again with no success.

All drivers are updated.

What I don't understand is this problem has been going on for some time, yet on the odd rare day Youtube sounds just fine??

Any advise would be welcome.