Well, PPro is a video editor, not an audio editor... so I have never tried just putting audio with no video on the timeline
But, having said that, I have read of problems with "some" mp3 files... with the solution being to convert to 48khz WAV
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:
When you go to Export, just choose Export Audio only, if you want no Video Stream.