When animating in Flash it can be sometimes frustrating, sometimes challenging, always interesting to try and export a good quality AVI (video clip).
Exporting an image sequence and then recombining the frames in post production software (VirtualDub, to build the AVI; Premiere or AfterEffects, to add the audio and editing) will produce the best result.
This animation tip may be handy for the second years animating in Flash.
Sometimes AVIs exported from Flash have unwanted junk pixels appear in the render. Exporting an image sequence is a way to beat this problem.