Try this guys! It helped me quite a lot. Still a bit present but way less than before

Looks like the game doesn't like quad-cores...

http://us.battle.net/d3/en/forum/topic/5051865438

BLIZZARD PLEASE FIX THIS THING COME ON!!! playing diablo 3 by disabling cores... wth?

i5 2500k 4.0Ghz
HD Radeon 6870
8 Go Ram 1600Mhz
600W Power supply