I have had the same problem. My ATI Radeon 5870 began the 99% activity at idle . I deleted the 11.3 driver version and went back to 11.2 driver with no problems... so far... Many of my friends have had the same problem recently and went back to the 10.2 version with no problem at all. It seems to be an update software problem with ATI. The newer version of CCC have automatic updates and that seems to be when the problems started, IMO.