Xerox 800 Waste toner on sheet in areas with light coverage

I am running a greeting card project where the back of the cards and the inside have little to no coverage. (2 up on 11 x 17) I am getting waste toner showing up on the sheet especially in those non image areas. We replaced the ibt belt cleaner a couple of times and it will go away for a few hundred sheets and then comes right back. It's especially heavy right after it stops to "adjust image quality".

Any ideas?

Thanks!