IMovie Audio Distortion (When Exported)

I recently made a video in IMovie, and I am running into some troubles with the audio when i export the video to a quicktime format or when I burn it onto a CD. I preferred using IMovie HD to the version I had upgraded to with iLife '08 so I re-installed IMovie HD - version 6.0.3. The video is about 40 minutes long and includes both video's from a handheld camera (with sound), still pictures, and music from my iTunes. The video runs great on iMovie, but when I burnt it to a DVD or when I export it to quicktime, it is distorting about 3 minutes of audio at the beginning of the video. It sounds like someone sped up the voices, put a mic in a wind tunnel, and made some weird sound effects over the top of the video. The original audio is still recognizable, but it is greatly masked by this distortion.

The other issue is that when I try to open the .mp4 file created from the "share" function of i-movie, it is giving me an error message that says "An invalid sample description was found in the movie". I have tried changing the extension to a (.m4v) but had no luck. When using VLC's video player to open the file however, it worked like a charm and the video displayed just fine (except for the audio distortion as mentioned above). Has anyone else run into this issue, and if so, do you have any possible solutions? I read somewhere online about separating an ac3 file (I have no idea what that is or how to do it), but I can not find the article again. Thanks in advance!