No sound in one event in iMovie 11'

I have lots of movies from my Panasonic camcorder in iMovie 11'.

All look and sound fine except in one event (with several movies in it) there is no sound.

None of the other events have the no sound effect so I am leaning toward it being a setting.

Does anyone know how to fix no sound in an event? If I add new clips to the event they also have no sound, but if I add to another event then I get sound. It is baffeling me!!

Please help.