This is the familiar powermizer related problem that has yet to be fixed. If you were running gkrellm you'd also have an annoying flicker every second. Has to do with the low clockspeed of the card and the Linux driver. Add the following to your /etc/modprobe.conf and reboot. This will lock the card at performance level 3 which should fix any annoying flicker while scrolling. I'm unable to get the Linux NVIDIA devs to acknowledge this issue as of yet, maybe you can go on over to the Linux forums and help out.
options nvidia NVreg_RegistryDwords="PerfLevelSrc=0x2222" NVreg_Mobile=3