Lines in graphics during games

Since connecting my Nvidia 7900 GT cards together with SLI i have noticed that during games (Age of empires III, Vietcong, but not Civcity:Rome) i get horizontal lines starting at the top of my screen. The lines reflect the color that is displayed behind them. It starts at about 5-10 of them, and gets worse, and reaches farther down when there is more activity on the screen. After trying to figure it out i found that they don't happen when im in 16 bit color mode, only 24 or 32.

My specs are:
Asus A8N32-SLI Deluxe
AMD 64x2 4400+
2 NVIDIA 7900 GT
2 GB Corsair RAM
680 Watt Themaltake PSU

Thank you for your help.

 

Open up your nvidia display and check if the "Show GPU load balancing" is selected under SLI multi-GPU. I have a similar effect with some games using the same cards. Unselecting this option has worked for me.

 

I've seen pictures of the gpu load balancing issue, doesnt look like it. It doesnt show up using in game screenshots or FRAPS so i took some digital pics of the screen.