AVI Recording, sound problem.

[TheImpulse]

I recorded my first clip which was like 35 seconds, it worked like a charm, everything was fine, half an hour later, I decided to record more of those and the video is fine but there is buzzing + sound, and really, a lot of buzzing, I'm not even recording any external sound, only one in game, so it really doesn't make sense, I tried switching to MP4, but the quality is really bad for me. How can I fix this?