some clips do not have audio in rendered project

[jdovi]

I've been using VideoStudio for years and recently upgraded to V10. My latest project required that I use about an hour of footage from MiniDV along with several short clips from my Canon digital camera. I rendered the file as an mpeg 2, 720X480, Lower Field First, 7000k. For some reason, certain clips within the final video do not have audio. I can't make sense out of why this is happening since it's fairly inconsistent. Has anyone else had this problem?