No Sound from Canvas Window

At first I would get a beep and a flash when I tried to play back my project in the Canvas window. Then I learned to use real-time so I wouldn't have to render until the end. Now I get video to play in the Canvas but no sound at all (including sound that is present in the original video clip and sound from an mp3 that I added into the timeline). No sound even though the video and sound tracks are showing in the timeline, and even though the sound will play in the Viewer window. Also all tracks in the Timeline are green-activated. Do I have no option but to render and wait, and then maybe discover that my timing in the added sound is out of sync with the video?

I have used iMovie HD with good success, but iMovie degrades my output video to a significant degree, which is why I invested in Final Cut Express.