Put your ear in the case and find out if the noise is coming from the PSU or the GPU. If it's the PSU, see what underclocking your GPU does. If the noise goes away, you know the it's a result of the GPU drawing alot of power.
I was going to ask if you had your rails balanced, but it seems that...
Innovation Cooling Diamond 7 is pretty good paste. It should never need to be reapplied, and there is only one paste that can beat it, but that paste wears out over time.