Slight pixel bleed - Samsung SyncMaster 701N

Hello. I recently replaced my GT230 with a GTX550ti and since then I've had a very small but extremely irritating problem. Basically, randomly while I'm running 3D full-screen applications (such as games) my screen (a Samsung SyncMaster 701N at 1280x1024) will go slightly blurry. I've looked at it very closely and it looks like the pixels are bleeding horizontally very slightly. I run many games without any antialiasing so it's very noticeable, although not very disruptive. I've tried everything to fix it, from changing my monitor's own settings to reinstalling drivers (with clean deletion), including messing about in the nVidia control panel. The only thing that seems to fix it is changing the refresh rate between 60 and 75Hz, but this is only temporary and the damn thing goes blurry again within minutes if I return to the game. Any ideas?

Try going back to the original video card? Seems like the issue is with the card not the monitor.