I have a Xante Ilumina (same engine as we all know) and it does the same thing. Don't know if the panel controls are the same, but try Menu/System Adjust/BG Setting. Factory default should be 0. I can't remember if you need to go up or down. Try both and see if that changes anything. I have a whole bunch of charge files that I drop in one at a time till it clears up. If I'm correct, I think it's a charge issue.
These Oki engines will print on anything you can fit through it. But it's a damn crap shoot if it will do it reliably with quality. One day it prints like a dream and the next day it just vomits toner all over the sheet, same temperature, same paper, same humidity. My Xerox is the opposite- it won't print on anything you can fit through it, but it will do it reliably with quality. My Wife has little b&w Oki machines in her office and they do the same thing.
