I second the chain noise nomination. However, I might put my 2cents in that the chain is too loose. Have you adjusted it since you got the bike home? It may have stretched. With only 400 miles, I dont' see why you would have taken it in for the 600mi service yet for the shop to have adjusted the tension . The factory Dunlops are a pretty decent compound, and you say they're properly inflated, so there shouldn't be any cupping or other deformation for them to be causing the noise.