The lines of grain don't always appear throughout entire levels of the campaign and not always in the same place either but when they do you'll know all about it because it looks awful and really hurts the visuals on display.
The first time I played through the campaign the lines of grain were there for the majority of it, and the last level looked terrible, went back and replayed a few of the levels that were badly affected and the grain had gone... only to reappear later.
The bottom line is it's a graphical bug that shouldn't occur and needs to be patched.
P.S.
Lorenso the troll should go live under a bridge because he's talking out of his arse, it's clearly a software problem and not hardware related given that exactly the same issue has been reported by a large quantity of people using a wide variety of setups.