No doubt the Flash veterans here will read this and chuckle "silly noob" to
themselves, but as someone who only uses Flash occasionally, I'm having some
problems.

I made a simple little animation where a bit of text is typed out, one
character per frame. For each frame, there is a key-click sound played. Once
I had the entire animation done, I copied the frames into a new movie clip
symbol. (There are 3 layers with 40 frames each.)

If I hit ENTER to play the timeline while editing the symbol, the animation
plays properly and the sound works fine.

If I exit from editing the symbol and go back to the main timeline, insert a
blank keyframe and place the symbol into it, then insert 40 blank frames, and
then hit ENTER, the animation from the clip plays properly, but there's no
sound at all.

What's the problem here? Why isn't the sound playing when the symbol is
placed into the main timeline?

Oh, and to clarify... the sounds are attached to keyframes.

The only ActionScript is on frame 41 where it says "Stop();" to prevent looping.