Why do Audio clips get truncated in Cp 9?

Hi, my Cp9 course features a dialog between two characters. Their lines appear as text boxes in word balloons, and the audio for each line plays when the text appears. At different spots, not always the same, the audio is truncated and the last word or so gets cut off. 

As a possible remedy, but to no avail, I increased the length of each slide to go a couple of seconds past the end of the last audio clip, and put in a "continue" button.  When playing the slide again, the audio plays perfectly, suggesting that there might be a caching issue or something.

Thanks in advance to anyone who knows how to solve this very vexing problem.

Dan