A scratchy stylus is a serious problem, the touch screen layer can be damage and the screen can become more difficult to see.

There are several things that can cause them and you should check these:

1. There is nothing stuck to the base of the stylus, this can normally be easy to remove, but if you have trouble try a damp cloth with some solvent.
2. The stylus is not broken or dented in ayway, the part in contact with the screen should be smooth and ideally round, if not you may want to consider buying a new stylus.
3. There may be dirt on the scree, try cleaning it.

Hope this helps. If none of these solve the probelm, the screen may have already been damaged too much, you may want to consider having it replaced.