Based on your avatar pic, they could be Cobra Speedster Shorts or HK American Classic Straights. Like Headguess said, check your exhaust gaskets and get new ones if need be. I bought my bike with aftermarket pipes and the guy who put them on didn't replace the gaskets. You can never count on the guy before you to know what he's doing.
Also, for the rattling (not sure if your whistle/rattle is two separate things), check all your mounting points and heat shield brackets to make sure they're tight.