@Steve - fwiw, I'm thinking that there might have been something happening in the conversion process when the editor imported that ended up producing sounds and anomalies that didn't phase. There's a ridiculous amount of editors that have no idea what they're doing and haven't the slightest clue about nesting sequences or using temp low-rez references properly. Not to mention simply setting up their session properly for post.
My other thought is that there might have been some level adjustments or processing the editor did on one of the two tracks that made them different and thus allowed you to produce this.
Based on the leftover frequencies I'm thinking some sort of craptastic compression happened somewhere.
Much to my chagrin, I once had a project where the editor (ne: producer/director) would render out sub-scenes as wmv's and then import those into a master session, edit those together and then render out his master. I shudder when I think of it.
In addition, I have two amazing 45m long recordings I made while doing sound design for the Dave Smith Tempest while force-crashing the OS from tweaking it so hard while using an unstable pre-release OS. I would make tweaks that too 45s-2m to show up (if the edit latched at all). It was pure analog oscillator, digital modulation routing anarchy. Amazing stuff, maybe I'll post a clip sometime soon.
This is after the OS was stabilized. It previously couldn't handle this extent of tweaking and the crashes are 50x more insane: Article: http://www.modulatethis.com/2011/10/first-look-dsi-tempest-drum-machine-roger-linn-james-kojac.html
Video from Article: [youtube]fnbspah_Zz0[/youtube]
I have so many recordings of weird happenstance occurrences like this from over the years it's insane. I'll be making a commercial library from them once I sort out get certain things sorted. I've been slacking a dealbit hard on that though.
I'm a big fan of feedback and extensive plug-in chains. Knowing my plug-in arsenal like I do, I know exactly what to insert where in the signal path to can get some insane and seemingly uncontrolled content within minutes.