Audio and Video Glitches, Skips & Echoes

I just upgraded to Vista, and I have been having some issues with the sound
and video.

I am running a Dell Inspiron 6400 with SigmaTel High Definition Audio CODEC.
I also have the Sound Blaster Audigy ADVANCED MB software installed.

Whenever I put in a DVD and watch it in Media player, every few minutes the
sound skips and echoes for a few seconds, then works normally again for a few
minutes. This repeats every few minutes. I have the same problem when
watching downloaded videos in WMP, or the DivX player, or any player for that
matter. Every few minutes there is a few seconds or glitching echoing sound.

Furthermore, I hear audio glitches during the startup music/jingle for Vista.

Any help with this would be great, as it is highly annoying!

Thanks!