Before playing back any sound, click the Enable Sound button in the Playback toolbar or enable it through the Play menu (in the top menu). This will ensure that you can hear the sound layers in your scene, even the ones included within symbols.
If there are two or more sound layers and you want to listen to them independently, you can disable the unwanted sound by clicking the Disable Layer button on the sound name layer in the Timeline view.
If you are trying to do a playback with sound and the frame rate doesn't reach 24 fps (frame per second), you can do one of the following to troubleshoot the issue:
- Shrink down the Camera view size to reduce the cached image size.
- Playback your scene without sound first, then add the sound. If you do not cache the imahes first without sound, the playback will try to follow the sound by skipping images that will never get cached.
- In the Preferences panel, in the OpenGL tab, reduce the size of the Playback Cache Size (in mb) preference.