Audio from video clips

What can I do to fix this?
You can check the source files and output files to determine if the audio was lost and, if so, at what point. MPEG-1 files, for instance are playback compatible in QT with audio. If you convert them, however, using QT or import them into iMovie HD, then they will lose the audio. On the other hand, if you have good audio in your project but export using QT compression but turn the audio compressor off, then your resulting file will be without sound even though everything was fine in the editor.

The conversions played sound in QT, but no sound in the editor... What can I do so I don't lose the audio?
Open the Event file(s) with the QT Player and check the "Inspector" window to make sure the file, as imported to iMovie '08, still has its audio track in tact. If it does and the missing audio is limited to scrubbing Event files, check the audio switch under the preview window to see if it is off. If no audio is present in normal playback/preview mode, then thumbnails could be bad and you might try re-thumbnailing the events. If the problem is on the project side, try duplicating the project and see if the duplicate has sound. If you still don't have audio, try trimming the duplicate project to a very short sequence and exporting it to see if the output has audio. This assumes you have audio everywhere else and it is not a system wide problem like muting, system sample rate switched to a different setting, system volume turned down, etc...