No audio when exporting to Quicktime

I am attempting to export a movie that has both silent clips and clips with sound. In iMovie the sound clips have the expected audio, but when I try to Export to Quicktime Movie I have no audio at all. My intention is to eventually burn this movie to a DVD to play on a stand-alone DVD player connected to my TV. FYI, I tried exporting numerous times with different option settings including (1) unchecking "Prepare for Internet Streaming", (2) Prepare for...Fast Start, and (3) Prepare for...Fast Start Compressed. None of these worked.