If you face difficulties with exporting sound from the FLA file this tutorial is a wonderful guide that will demonstrate you the process in detail. Step by step instructions and video tutorial will be your keystone to success.
1) Open library in the .fla file, by pressing F11 key on the keayboard.
2) Arrange library items by "Type"
3) Scroll down to the end of the library, there you’ll find all the sound items
4) Copy the sound item you wish to export
5) Create a new .fla file. File -> New (hotkey CTRL+N)
6) Now right mouse click anywhere on the stage of the new .fla file
7) The sound will be embedded into the first frame of "Layer 1". Select that frame and hold down F5 button on the keyboard to add more frames to the timeline
8) Add the frames till you see that the sound wave has ended. Remove any empty frames from the timeline
9) Now export the sound File -> Export -> Export Movie. In the dialog window, set "Save as type:" option to "WAV AUDIO" and press Save button
Feel free to check the detailed video tutorial below: