The fan on my 7870 all of the sudden won't spin up past ~15-20%. Whether I try to manually adjust it or let it stay on auto, the fan won't spin up. Occasionally when I try to manually set it to 100% it will sound like it is spinning up and then die back down and it will repeat that over and over again. Anyone know what is causing this? This happened to me once before and as quickly as it came, the problem went away.
Notice the fan tachometer reads some ridiculous numbers even though the fan is actually idling.