My ground textures are 'jumping around'

Its a bit hard to explain... but for some reason when I am just sitting there with the camera still and looking at the grass beside the runway, it starts twitching around.
The ground textures also look a bit victim... as you can see here:

and my system isnt exactly weak, especially not in the graphics department. 512mb 8600GTS graphics.. 2gb RAM, 1.8Ghz dual core
any ideas? I cant remember what ground textures I have on... but the ground details are set to max
cheers
The ground textures also look a bit victim... as you can see here:

and my system isnt exactly weak, especially not in the graphics department. 512mb 8600GTS graphics.. 2gb RAM, 1.8Ghz dual core
any ideas? I cant remember what ground textures I have on... but the ground details are set to max
cheers