If you guys have no problem with the nozzle check, and these lines are in the same direction as the printhead, I'm guessing it might be some sort of feed adjustment that is necessary. Since this is also just on canvas, this makes me suspect this even more. Each time I print on canvas, the paper feed isn't as precise. I've never had to do this myself, but I understand there is a way to have the printer run a feed adjustment on each paper type. It seems like these little lines are just gaps inbetween the scans of the prinhead as its going back and forth and perhaps adjusting this to feed ever so slightly less would fill in the line. This is just a guess though.