If it is feathers, it is probably making contact with your hand where the tip of the quill is glued to the shaft. Sometimes the tip of the quill is not glued flat to the shaft, and that can play havoc with your hand. Other times, there is not a smooth transition between the quill and the shaft. Make sure the end of the quill has a gradual bevel; if not, trim it into a smooth bevel with a razor blade or sharp knife. Then put a dab of glue on the end of the quill where it meets the shaft. When the glue dries, burnish it flat with the back of a teaspoon or something.
If it’s the string, raising the brace height should solve the problem.