When you insert a sound file into PowerPoint, a speaker icon appears in the bottom-right corner of the visible slide. A speaker icon indicates that a sound file is either linked to or embedded in the visible slide. 

You can configure this sound file so that it loops repeatedly until you end your slide show or advance to the next slide. 

To do this, right-click on the speaker icon and select Edit Sound Object from the resulting shortcut menu. 

This opens the Sound Options dialog box (Play Options dialog box in PowerPoint 97 and 98). Select the Loop Until Stop check box in the Play Options panel (Movie And Sound Options panel in PowerPoint 97 and 98) to loop the sound. 

Next, press [F5] to launch your slide show. Advance through the slides as you normally would. 

When you reach the slide containing the sound file, click on the speaker icon (unless you configured the sound to play automatically) to initiate the sound.

To stop the sound from looping, advance to the next slide or press [Esc] to exit your slide show.