Problem with sound on music when posting to YouTube

[MitchT]

I've posted a piece of dance music that I made to YouTube, but it sounds terrible - there's an odd "scratching" sound in the background. The sound is perfect on the original so it's something in YouTube's conversion process that's causing it. I'm exporting from iMovie and have tried all sorts of combinations of settings, but they're all as bad. Does anyone know what exact settings to use in iMovie to avoid this problem?

Here's the track...

http://www.youtube.com/watch?v=rhoBF7HAcK4