Doesn't the fan use one of those silly little GPU fan connector's?
Is it under warranty? You could complain to XFX customer service but good luck with it I have found with GPU's XFX are a joke. They sent me back my card unchanged and warranty expired on it's way back to me. GG XFX.
Could see if there is anything touching the fan? Opening it will void warranty though.
135mm fans are not very common...
Apparently they have 5 year warranty?
"2 year standard warranty with all PSUs - simply register your PSU when purchased at http://xfxforce.com/en-gb/Help/Support.aspx to obtain a 5 year warranty.
Register within 30 days of purchase, and provide proof of purchase for any warranty actions."