Version pro18. When editing MP4 files the audio travels on the time line. There is no visual representation but the audio will repeat a section of audio on various places on the timeline. If rendered it will appear in the render. A simpler way of describing it is pieces of the audio that is earlier on the timeline will randomly show up later in the timeline and replace the audio that is there. 2 seconds in length. There might not even be any edits and this happens. I transfer video tapes and just cut the ends off the videos. Virtually no editing. I can move around the time line and audio from much earlier on repeats itself. Very odd.