When i had my 1990 300zx lowered with eibach lowering springs it did what I'm experiencing with feathering on my 350z. The fix for me and widely used by other zers at twinturbo.net are these http://300degree.com/hard_parts/camberkit/. Probably not the same problem but i thought i would post it anyway. This noise is terrible.
One other question. The dealership told me that my 3 year warranty would start from the day i bought my car. Is that usually how it works with buying a used car from the dealer? Cause I'm comming up on my 2 year anniversary from when the car was originally sold. Later

 

Yeah the bumper to bumper warranty is good for 3 years from the date the car was ORIGINALLY purchased from a Nissan dealer. Whether you buy it new or used, that is the way it works.