Try these tweaks to make the audio files audible:
1) Make sure you have downloaded this .mp3 audio file plugin: apple.com/quicktime/
2) Check Quicktime preferences to make sure .mp3 files playback is enabled:
To do this, open Quicktime. Click on Edit > Preferences > Quicktime Preferences. Under the Browser tab, click MIME settings. Make sure the MP3 checkbox is checked.
Also in Quicktime Preferences, click on the File Types tab. Make sure the box beside MP3 is checked.
If none of this helps, email me.