I have to admit up front that I'm not sure exactly how to solve this problem, but you can gain a lot of important information about your audio files, and ascertain whether it's clipped data or not, by doing this:

When you can see one of your audio file objects, right click on it. You'll then see:

Now, from this point, choose Sound Options and you'll see:

Notice here that it shows the total playing time of the audio clip (mine is 5:09). Does yours show :00:01?

Here's some useful information from the PowerPoint help system too:

You can insert sounds in the following formats:

• Audio Interchange File Format (AIF, AIFF, AIFC)
• Apple QuickTime Movie Sound (MOV, MOOV)
• Apple System Sound (SFIL)
• Apple System Resource Sound (RSRC, rsrc)
• CCITT A-Law (European Telephony) Audio Format (ALAW)
• CCITT U-Law (US Telephony) Audio Format (AU, SND, ULAW)
• Microsoft Windows Waveform (WAVE, WAV)
• MPEG Layer 3 Audio (MP3)
• Advanced Audio Coding (AAC): MPEG-4 Audio
• Musical Instrument Digital Interface (MIDI, MID, KAR)

Tips

• Some sound formats, such as MP3 and MIDI files, and files with a file size larger than the size set in Preferences, are not embedded in the presentation when you insert them. Instead, they are linked from a location on your hard disk or the Internet. If you move the presentation, make sure to move these sound files with it. To make sure all linked files are included with your presentation, save the presentation as a PowerPoint Package.

• If the sound format you want to use is not listed here, you can still play the sound from a presentation by creating a hyperlink to it. Make sure that you have a sound player installed that is compatible with the sound format you want to play.

I wonder whether the separate files on disk feature of larger audio files is what's affecting you, actually. Check to see if that's what's going on?

Hope that helps you crack this problem!