When importing clips into iMovie HD's timeline, the first few frames of audio cannot be removed.

We've tried importing with no sound, zeroing out the audio of the clip, and extracting the audio to no avail. When listening to the extracted audio by itself, there is no sound - but it is still at the beginning of the video! We've trimmed the video intro, split it into separate clips, put a transition at the beginning of the clip, and reimported the video (multiple times). This is on several different clips (but not all) from the same camera, same tape, same shoot.

Any idea on how this problem can be fixed? We're going crazy.