i have sapphire hd 6670 vga edtion 1gb ddr5 on my system ... when i use my system for little bit more say for 5 to 10 mins its gpu clock automatically jump up to 800mhz from 100 mhz and its memory clock speed jump to 1000 mhz from 150 mhz and shows 98% is on load but my system is running ideal... why this is happening????