I guess that unease is the reason I didnt express the feeling I wanted correctly. The feeling that "unease" transmits varies from person to person, from time to time. Maybe if I use the song in a game or an animation with story, I can guide the feelings a bit better to where I wanted them to in the first place haha.
You can either drag&drop the sound file (I usually use mp3 or wav) into the flash library or go to File > Import > Import to Library... then add a new layer, click on the first frame, on the preoperties panel go to the "Sound" tab and on "Name" select the sound you imported, then change the Sync to "Event" if its a sound effect, and to "Start" (not synced to the animation) or "Stream" (synced to the animation) if its music. Hope this helps ^^