I've got a Patriot Dually as well that I picked up used. I am very familiar with the sound you are referring to. Basically, since it is such a radical cam when you drop into the nearly non-existant valley it is so sharp that you slam your draw stops into the string. Through practice I have been able to control my draw so I don't slam as hard into the valley, but it takes time and practice. I still do slam it back every once in a while, but I'm hoping to get it under control in case I need to use the bow for hunting. Right now it's a back-up. Take some time and work on drawing it slowly and evenly and you should be able to at least reduce the noise you hear.

Good luck.