[Larold]

I will start with the stupid stuff that I have encountered.

Is it on the Dialogue track? I mix music and sometimes there is an odd sound effect or rumble that they left in by mistake.

Do you have a plug in that automation starts up, like an analogue mixer? Sometimes, the default setting starts with a 50 or 60HZ hum to make it sound like real analogue gear, like on a Bomb Factory 1176.

Let's start with that stuff. If you are doing the score, and it's on the dialogue track, simply mute it while you work, and alert the Post guys, or contact the production office. Sometimes, the videos are made by interns in the office and they mess up.

I know you said this happens only during a bounce. I assume it's actually printing, right? I would also try muting things one at a time until the problem is found. It isn't black magic...just trial and error. Good luck.