Sorry Alex, been so long ago (3 years?) so I cannot remember what I had to tweak to get rid of it. Have you ran the GTR2 graphics config thingy?
in mine I have shader level set to auto
Full screen anti-aliasing ticked at level 5
vertical sync on
just looking in my NVidia Gfx settings for GTR:-
,
I have anisoptric and anti-aliasing set to application controlled.
FXAA off,
transparency off.
Texture filtering - Quality
Texture trilinear optimisation - on
Triple buffering off
Vertical sync - application controlled.
Hope that helps!