A simple iMovie question:

You can probably find the answer on a forum

I've got  iMovie HD 6.0.2 (267) 

When I attempt to superimpose a title
on a piece of video it completely 
scrambles the underlying audio track.

I follow the instructions in the manual, the 
rendering takes place seemingly normally, but 
on playback the audio is completely messed up
(sounds like it's been fragmented.) 

What's going on and how do I fix it?