stream is the sync property that should cause the timeline to sync with your sound.
i'm not sure if your use of start and stop are causing a problem.
Yes, using the "Stream" property is correct, but that is only part of the solution.
It's a very common misunderstanding to say
my sound still does not match to the scene (or to the frame)
... as though somehow it's the fault of the audio that the two don't sync properly.... when in fact it's the fault of the animation or video content that it does not sync with the audio.
Here is why I say that... the audio portion has to be played back at an exact speed (sort of like frames per second) to maintain the original sound. Slowing that playback speed down will decrease the frequency of the audio... giving it a slightly lower pitch. Playing the audio back at a faster than original speed will increase the frequency of the audio.... raising the pitch... the method used by "Alvin and the Chipmunks" to give their unique sound. Flash does not slow down or speed up the playback because that would change the pitch. Flash plays the audio back at the original frequency.
So what it boils down to is that you have to match the animation to the audio... NOT the other way around. You have to select the exact frames per second (for playback in Flash) that will give you the exact same length of time of the original audio. For example, let's say you have a 60 sec. mp3. If you use a fps of 30, then your timeline should be (60 x 30) 1800 frames long. Then you work you animation to fit inside those 1800 frames.
But if you set up your animation on a timeline of only 1500 frames, then the audio will seem to lack behind the animation (because the animation uses up all it's frames before the audio finishes playing).
If you set up your animation on a timeline of 2200 frames, then the audio will seem to run ahead of the animation (because it runs out of frames before the animation is complete).
If you are matching audio to a video, setting the Flash fps rate to exactly match the video will usually give very good audio/video sync. So for example, if the video frame was 29.97, set the Flash fps to exactly 29.97.
Here is an example of a video embedded directly in the main timeline which has the audio synced just fine... using Flash frame rate that exactly matches the original video frame rate.