Maybe you struggled above a bug of msp, which I noticed sometimes:
If you scrub in the timeline you may hear sound at wrong positions. Seems to happen most often after deleting part of a video in the timeline. If you switch on waveform display mode you may e.g. hear sound where the waveform displays silence. You may even hear sound past the last video! This is very irritating if you want to cut your video e.g. after the end of a sentence.
I believe it has to do with smart rendering and perhaps its also hardware dependent.
To work around I usually switch of smart rendering and force rendering of the part of video in question.
I meanwhile allways switch of smart rendering when creating the final video file. I found that this safes me more time than using it.
