It could be a number of things -- depending on how the DVD was created.
Also, when you started your Premiere Elements project, did you select the project settings for Hard Drive Camcorder? This is important when working with DVD files.
You must also let the files fully conform when you bring them into the program before you start editing. Did you do this? You can watch the conforming progress in the lower right corner of the program.
Thanks so much for the prompt response! How do I ensure that the files are "conformed"? I will try what you suggested and let you know.
When you Import the VOB (or other files), you will get a progress bar in the lower-right of your GUI. This ARTICLE will give you some info on Conforming.
This ARTICLE will give you some background on VOB files, in general.
This ARTICLE will give you some general Audio tips. Maybe something there too?