This may sound like a dumb question at first (maybe it is) but on an 80mm case fan, what is actually 80mm? Is it the casing the fan is in or is it the hole it moves the air though? Basically what size diamitor should the hole you put in your case be? The full 80mm or just a bit smaller? I currently have access high quality 72mm hole saw. Would the 8mm of over hang cause noise problems?