moar vidding woe - phantom sounds in final cut divx exports

So I have had this problem with Final Cut for a few months where if I use the Export as Quicktime conversion --> export as divx option, it repeats a random snippet of the music right at the end of the vid, i.e., the song will fade out and there'll be a one note blast right at the end.

I have previously had two workarounds with this - either just open up the file in Streamclip once I'm done and rexport as an avi with the last second or so cut off, or export from Final Cut as a huge quicktime movie -- where there's no audio problem -- and rexport as an avi from Streamclip.

However! For my current project this isn't working, because however I export from Streamclip, some sections of it come up all pixellated and unpleasant. So now I am trying to figure out why Final Cut does this in the first place, but am drawing blanks. Anyone got any suggestions?

VID: Tightrope (multi-fandom, for halfamoon)

Tightrope
by such_heights
fandoms: Avatar: the Last Airbender, Battlestar Galactica, Doctor Who, Harry Potter, Merlin, Star Trek XI, Stargate: Atlantis, Torchwood.
characters: Katara, Mai, Anastasia 'Dee' Dualla, Cally Henderson, Tory Foster, Rose Tyler, Martha Jones, River Song, Molly Weasley, Ginny Weasley, Guinevere, Nyota Uhura, Jennifer Keller, Gwen Cooper.
music: Tightrope - Janelle Monáe
content notes: none
summary: You dance up on them haters.
download: 22MB .avi direct download | subtitle .srt
notes: Made for halfamoon, the annual celebrations of female characters. Many thanks to eruthros and dharmavati for help with source, fly_to_dawn for the beta and hand-holding, and everyone else who offered tech help and put up with me tearing my hair out.

( embed and lyrics )