I've also had this for months and months. Have a Nvidia card also. Tried so many things too numerable to mention but never had any success. Got so used to it that I'm not sure if it's still there. Will check.
Edit. Have now rebooted and the garbage is not there. It must have rectified itself, possibly over the last 2 updates.
Asus M4A79XTD EVO motherboard, AMD Phenom II X4 965 CPU, 4 GB ram.
Gigabyte NVIDIA 9800GT Silent graphics card, Dell FP2007 22 Digital Flat panel.
Samsung harddisks 2 x 200gb SP2004S,1 x Hitachi 750gb HDT 72107,Optiarc SATA DVD-RW. Sabayon 64 & 32bit.