All above is true, but also consider that brandy new sprockets and chain take a while to wear in. The sprocket teeth and inner sideplates polish up, and the chain "stretches" (actually pin wear) to the correct length. Also, what are you using for chain lube? If you want quiet run phil tenacious oil. Draws dirt like a mofo though. Dry lubes are noisier. Tri-flow is pretty quit too. Note that noise is probably NOT the most important consideration when choosing a chain lube, but it does make a difference.