The best thing for you to do is contact Pinwheel 12 through this sight. He is the head of Merlin USA, good guy, and is the best person to help you. There are so many things on a compound bow to vibrate and rattle it's amazing we ever get them to shut up...
I'm shooting an XT with Viper cams myself and don't have any complaints on vibration as long as I don't screw up. I would guess it's probably a tuning issue or your shooting form. Pinwheel 12 will help you with the "hardware", the shooting form is up to you. Are you gripping the bow tightly? If so, try a looser grip and a bow-sling. Do you have a nice clean release and follow-through? I know if I'm tired and start letting my form fall apart I do feel more vibration and the bow is louder, but it's "operator-error" not the bow. Might not apply in your case but the better you shoot the better the bow will perform. Do this little test...rap the bow hard with the palm of your hand up and down on the riser, especially around the limb-pockets. Do you hear any vibration or rattleing? Try and pin it down if you can, it might just be something loose.
I should add that I have been using an old cobra 6" 12oz. stabilizer with a sims stabilizer module in the front and a short Doinker Chubby Hunter on the back of the riser. They did reduce the riser vibration, but it really isn't bad without them. I've tried an STS and have mixed feelings about it. I like the way it would keep the string off my arm wearing heavy clothes, but if anything I thought it made the bow noisier, or if not noisier, more harsh sounding.
Good luck, once you get that XT tuned up I'll bet you will be happy...
