Can't hear loops in Apple Loops Utility

Hi all, I have a very strange problem with Apple Loops Utility: in the Loop browser, everything is fine, I can audition blue and green apple loops and they play ok in my tracks, too, along with all other audio and MIDI. But when I open an audio file in Apple Loops Utility and try to play it from within the utility I can't hear anything! I can see the waveform with all the transient markers etc but no sound. So far, I haven't found anyone with the same problem but I hope there's someone out there who can help as this is very frustrating. Many thanks in advance, Beene