Welcome to the forum.
I agree with John T., regarding some MP3 material. See this article: http://forums.adobe.com/message/4146900#4146900
If you are having issues, when using Audio, but no Video, you might want to try one of two things:
- Create Black Video (from the New Icon), and place that onto Video Track 1. Extend that to cover the music files.
- Create Transparent Video (from the New Icon), and perform the same operation.
When you go to Export, just choose Export Audio only, if you want no Video Stream.