Problem getting audio on imported video clips

I use a JVC Everio Camcorder (model GZ-MG750).

I have downloaded my videos onto my MacBook Pro using the USB cable which came with the camera (I did not use the software disc the camera came with).

I have iMovie '11 installed onto my machine (version 9.0.7).

The videos have been imported into iMovie, however, I cannot get any audio from the clips (when the videos are watched back on the camera itself, there is audio).

Any help would be greatly appreciated as I have been playing around with this now all day.

Many Thanks