Exporting as an MP3 file results in the playback looping or duplicating a small portion of the audio file. Typically it loops a piece from the end of the file. When playing back from QT 4.0 results in a -40 error and will not playback.When playing back from QT 5.0.1 posts a -6006 error that says playback may be "messed up". It gives the option to continue or cancel. If you continue play back is as described above.When playing back with QT 5.0.2 no error is posted but the MP3 plays back as described above.