to 3d shoots.
First thing I would look at is the string stopper, they will cause some noise if spacing isn't right. Should be just able to fit a credit card between the string and stopper. Next take a real close look at the bow and see if anything is starting to loosen up. Witha loose grip on the bow, start at the top of the bow and start hitting it with the palm of your hand and work your way down, if there is something loose or vibrating that will help pin point the problem.
Let us know what you find.