As an update....

I found in the Animations section / Transition Sound. If I look at the drop down selection I will find the corresponding audio file name, however, I cannot find any of these files (an example of one is 182-192.aif) I have searched the comp and no luck finding the file. I suspect this .aif is associated with one of the .wav files, as I can count the number of files in the drop down and there are same number of .wav files, I'm just surprised they are not named the same. There are also selections in the transition sound drop down such as Chime, Cash Register and Drum Roll - which I suspect are standard issue with PPT.

At least now I know how to remove the existing audio track from a slide or set of slides by selecting No Sound and adding a new sound clip to the slide