Thanks for responding.
The MPEG1/2 Audio is selected for the titles. I have no problem playing the source video and audio from the DVD using Windows Media or VLC Media. In fact, DVDFab has no problem playing the source video and audio in its little video preview window at the bottom left of the application window.
The problem is when I merge the titles in to one on to a balnk DVD; I get the video but no audio.