Hey man, I was having the same issues. Anyways I ran into this post and it solved my problem (played fine when I tested it as a scene but the sounds were off by a 1000 frames when exported as a movie)
If you see TheL1st, thank him:
put your sounds in seperate movie clips, ino it sounds like a pain but its necessary for good flashes
this removes ALL syncing issues because the sound cant get ahead of itself if it doesn't exist yet