Hi there

I'm trying to record some videos through Quicktime using my macbook isight and the built in mic, but it seems to have this kind of squeaking noise in the audio. It's not feedback, because I'm wearing headphones, and for some reason it doesn't come up as much (or at all if I can notice) when I record audio on its own. I have noticed that it happens a bit in skype, but it's not feedback because I'm wearing headphones in that situation too. What could cause this?

I made a quick recording of it:
Movie 4.mov

I really don't get why it's doing this, and because I'm trying to record music, it's frustrating.