I did a test, full black across the width, the issue begins roughly 2' from the right and gets worse as you go left.
Ran the same test on both Epson's, and one has it on the right, and one on the left.
Called Epson, they said it could be over saturation of ink.
Talked to my Tech, is says its mechanical.
He's coming by tomorrow to check, we shall see....
Oh and it happened in both ONYX and Colorburst.