What a bummer...nothing really comes to mind. It coud be something with Plural Eyes (I know some people have had similar audio-mangling problems with Plural Eyes).
You mentioned everything is panned center...just to be sure, is the MASTER audio channel also panned to center?
Yup - ALL Channels panned to center. I had been using things after the Pluraleyes sync for a few days before this manifested, so I don't think that's it (good to know about though).
Thanks for the effort - I'll update if I find out anything here.
It would be nice to see the screen shot of your timeline. Just curies how is you audio ended up on the timeline.
Since the Plural Yes give a mono tracks you could right click on each one of them and disable it, so it will not play, Also you can change the audio level on each one of them separately, if they are unlinked.