Audio problem on FCP

I've come across a strange anomaly when importing movie clips into FCP (10.1.4).

Background sounds, such as people talking, sound 'squeaky' (for want of a better description) and distorted. Foreground audio somehow seems less affected.

Any added audio, such as music, is OK.

To add to the puzzle, the audio in the same movie clips imported into iMovie are perfect as is the audio when the same clips are played back in QuickTime.

Any clues anyone, please?

TonyT