Get rid of your fans, If they are 80mm throw them out, Get 120mm around 1300RPM fan, then your set. 120mm fans give out just as much cooling as an 80mm fan just at a slower spinning rate meaning isnt as loud
to be honest i don't really feel like drilling haha, i only have room for an 80mm, which spins at about 1400/1500rpm which is fine by me, i noticed absolutely no sound difference after putting it in.