I've had this happen on occasion in the past, but I can't seem to remember what I had to do to fix it.
There is a point in the video I'm currently working on that if you play it back anywhere from a few seconds before that point to the beginning of the video, when it hits that spot the audio suddenly freaks out (sounding something like a semi's horn). You can still here the dialogue under the noise, but the music is gone.
It only occurs when both the music and dialogue are both playing back. If I turn either one off, there's no problem. It happens right on a dialogue cut.
If I stop playback and start again, it's gone. If I start playback right at the beginning of the dialogue clip, there's no problem. If I don't stop the playback, it continues on, right into the next piece of music and dialogue.
Ok, I think I may have figured out what was causing the problem. I had the music track locked, when I unlocked it, the problem went away. Not sure why locking an audio track would cause this problem, and only at a specific area, but it hasn't occurred again.