Hi, i recently bought a new XpertVision 8500gt super, all seemed to be going well as in, it runs all of my games perfectly, but recently the fan on the card has been making a very very loud grinding sound from time to time and the sound slowly gets louder and the fan gradually comes to an almost complete stop. there is definately nothing stuck in the fan and sometimes it does work properly. I have sent it back to be repaired, they sent me it back and it still does it... any ideas on whats wrong?