nukeproof generator

 it is probably a the seam plate. it is a plate that is pressed into the rim before they weld it to hold everything together while they weld it. this piece is usually not needed for anything after the welding though. mine came loose on my rims also i ended up putting a little Caulking glue in it to hold it from rattling. usually they are located exactly opposite of the valve. make sure you clear all the glue of the nipple areas before it dries even if you don't it does scrape away real easy.

 Thanks, that worked.