[Gary Tyson]

I had the same problem, then noticed someone here wrote ‘turn off the noise reduction’ that I had applied to the track from one of the cameras (using only 1 source audio as normal), and that seems to have fixed it instantly, so I didn’t have to restart the edit (2 hour edit) with over 400 cuts in it….phew.

So from my experience, if you have applied some audio effects, maybe them thats causing it, as I noticed I didn’t have the issue before i started tweaking the audio either.

Hope that helps (using FCPX).