Ive this Grain Bug too and its unplayable!
Especially the 3D mode is a NoGo with this Bug. Even the Film Grain itself (On Console) is Way too much in my opinion.
The PC Version looks so clean and runs smooth in 1080p 2xAA/16xAF Medium Settings on my Mainstreamsystem with Core i5 750, 4GB Ram, and HD5770.
Meanwhile i play it on PC with the wireless Xbox360 gamepad (Controlls are exactly the same as on Xbox360) on my 46" FullHD and it looks awesome! So smooth without any Perfomance Drops, great Engine Crytek!

The Xbox360 Version still looks very good
until the Grain Bug appears. Then it looks like Crap.
I cant understand how Crytek can release a Game with such a heavy Bug! Fix it, otherwise its a shame...