A rattling noise at idle is almost always a worn supercharger coupler inside the nosedrive. Refer to How they work for a description of it'* function and purpose. The noise comes from the 6 holes in the coupler being worn into more of an oval shape than round. Don't confuse this noise for a noise from the harmonic balancer (dampener). The balancer makes more of a loud clattering noise at idle. To determine if the rattling noise at idle is your problem, remove the supercharger belt (by releasing the belt tensioner) and rapidly turning the supercharger coupler back and forth rapidly by hand (back and forth in the direction the belt normally spins the pulley). If you 'feel' any slop or movement without feeling the immediate resistance of the weight of the rotors spinning, your coupler is worn and should be replaced. Generally, if you notice the problem is just beginning, it'* not critical that you replace it right away, but plan on it soon. Refer to rebuilding nosedrives for procedures on changing the coupler yourself. This is a good time to totally rebuild your nosedrive if you feel you're up to it, but isn't always necessary unless you have bearing related problems also (great preventive maintenance, I suggest a nosedrive rebuild if you're changing the coupler). For M62'*, you'll need to remove the entire supercharger from the car. M90'* can pull the nosedrive without removing the supercharger.

Grinding or excessive whining noises are generally a bearing issue (or your kids in the back seat). Use a mechanic'* stethoscope to determine where the noise is coming from. Keep in mind that some whine from the supercharger is normal due to the straight-cut gears in the nosedrive. This can become more prominent after changing to a smaller pulley or building a custom air intake. The supercharger or something nearby? Refer to Google for a typical warnings. Try a Google search on "how not to get your stethoscope tangled in the belts of a running engine". If the grinding or whining does seem to be coming from the supercharger, you'll need to remove the belt to diagnose further. After removing the belt, gently and slowly turn the pulley by hand, feeling for any roughness or grinding. Also move the pulley in and out if you can (as if you were trying to pull the pulley off the shaft or push it back on). Any slop or play in this direction is another indicator of bearing problems. If you find any bearing failure indicators with these tests, plan on either getting a rebuilt nosedrive/supercharger or rebuilding it yourself. Even if you're sure it'* only the nosedrive bearings, it'* a good idea to go ahead and replace the needle bearings in the supercharger itself also.