Take a look at this link.

https://www.youtube.com/watch?v=kH8spGRL3Yk

This method works on the AMD Reference Card "Squirrel Cage" type fans. It is as easy as it appears in the video. I have used it on my 5850 and 5970 Reference Cards. I use 3 dessert spoons as levers instead of the screw drivers shown in the video. Once you pop the impeller off you will see why the "drilling a hole" method can work but its really not a long term fix, and you do need to get the hole in exactly the right position.