Document every occurrence of the 'nuisance' behavior, of what you say and/or do, of what your neighbor(s) say or do. Keep copies of all letters.
1 Legal Term. We are entitled, by law, to the quiet enjoyment of our home. If we are renters, our landlord is responsible for making sure we have quiet enjoyment also.
2 How to Get Neighbors to Turn Down the Noise, by Cora Jordan, Copyright © 1994 Nolo Press
Please note: The behavior that is bothering you may not be considered a nuisance under the law. You should still try to work things out with your neighbor. Try talking and/or mediation. There may be something that can be done so everyone is comfortable.