Don't quote me 100% on this, but I remember someone else mentioning rattling coming from the pulley. I think that means the bearing is bad. Code3 has replacement bearings listed on their site as a fix for the rattle.

http://shop.code3performance.com/pro...=5&productId=5

If you're just putting the Code3 pulley on for the first time, you shouldn't have a bad bearing already. I would think that Brandon at Code3 would send you a new bearing free of charge.