Explanation of blower noise:

When new an Eaton has .0025 rotor to case clearance.  (.0025 is equal to the thickness of a piece of paper.)  With that said it is easy to understand that when you assemble all pieces a joined to the blower it is going to pull the case somewhat out of round.  The same scenario as bolting heads on your block the cylinders are pulled somewhat out of round this is why your machinists will recommend you hone your block cylinders with torque plates to simulate this stress.  This technique can not be used on blower cases-So exact torque specs and tightening sequence’s are critical.  

We do many different styles of Eatons and all have their rub areas they are consistent case to case.  The pictures below are stock Cobra and Lightning cases.  
Picture 1
Picture 2
When you look at the Cobra case you will notice a Shadow at 3 & 9 O'clock this is common to every Cobra.  The shadow was made by the rotors rubbing the case due to torque stress.  There are many of you who bought your car new and may or may not have noticed this because it eventually went away and you forgot about it.  It generally takes about 1500 miles to break in.

Because we know why, when and where this occurs Stiegemeier Porting has taken additional machining steps to add clearance in these rub areas.  The Cobra rub is in a very critical area I do not want to over machine this area because of performance.  At times a customer may still have a slight rub after a rebuild and re-torque but I assure you it is less of a noise then when your car was new.  It will just go thru a normal break in period.

Another noise which is bad and should not be ignored is a rear case grind. Picture 3 shows this at the rear of case-.  This happens when a pulley is installed incorrectly.  Always have your pulley installed at the time of porting service.

Most often a noise that is constant and does not go away is an idler pulley bearing.  A good check is to lubricate one idler bearing at a time restart the engine and listen.  If you have a loud whistle coming from your K&N it is bypass valve flutter.  It is better to control the valve thru the tune and not the vacuum lines.  Do not do both.

Every Lightning blower case has rotor rub at the rear of the roof.  Anyone in doubt just remove your plenum and feel the roof.  
Picture 4
Picture 5
Picture 6
This is not a critical performance area so we machine the added clearance needed.  Never run a phenolic spacer between a Lightning plenum and blower, this will cause extra heat to remain in the blower case and failure will follow.  The rotor stripping on the Lightning's has been 100% positive with no power loss and zero failures.  Cobra rotors do not flake and rotor stripping is not required.