Do you have the slides set to advance automatically, but the sound is only on one slide... making the slide show wait for the sound clip to end? If that could be it,...

1. Select the sound icon on the slide.
2. On the Animations tab, in the Animations group, click Custom Animation.
3. 
4. In the Custom Animation task pane, click the arrow to the right of the selected sound in the Custom Animation list, and then click Effect Options.
5. On the Effect tab, under Stop playing, click After, and then select the total number of slides on which the file should play.

Note The sound file should be as long as the specified display times of the slides. You can see the length of the sound file on the Sound Settings tab, under Information.