You are most likely having render time issues (aka, the flash is too big for its own good and the computer is having problems rendering it correctly).
1) Save and Compact through the File Menu.
2) Restart your computer.
3) Disable any other programs you do not need.
4) Rerender.
If the Flash is still buggy, try a few of these steps.
5) Consider the elimination of scenes. Scenes screw up flash a lot, especially with sound and programing.
6) Turn on Streaming if you haven't already; it will lock the sound to the timeline. This can be done through clicking the frame with the sound, and extending the properties panel and finding the "Sync" dropdown.
7) Give the file to someone else to render.
8) Check your library for excess garbage. To turn on your use counts, go into the library panel (ctrl+L) and find the menu button in the top right section of the panel bar. Select “Keep Use Counts Updated” and it will count all the library items that are used. Note that it will only count objects on the stage, and will not count objects loaded through actionscript. You can use this tool to figure out which symbols are junk and can be deleted, which can be extremely helpful.