How to Play a Sound Over Several PowerPoint 2007 Slides
Sometimes, you want a PowerPoint sound file to play while you display several slides in your PowerPoint presentation. PowerPoint stops a sound when you move to the next slide. You can alter this behavior in two ways. First, if you want a sound to play from the current slide all the way to the end of the show, select the sound, call up the Sound Tools tab on the Ribbon, and set the Play Sound option to Play Across Slides.
If you want more control over how the sound is played, follow these steps:
Select the sound icon.
This calls up whichever sound you want to edit.
Choose the Animations tab on the Ribbon and then click Custom Animation in the Animations group.
Click the down arrow next to the sound item and then choose Effect Options from the menu that appears.
This action summons the Play Sound dialog box.
Select the After option (in the Stop Playing section) and then set the number of slides you want the sound to play for.
When you count the slides, start counting with the slide the sound is on
(Optional) Right-click Effects Options to open the Play Sound dialog box, and click the Timing tab.
Set the Repeat option.