Your home is indeed your castle, just as the expression goes. It is your place of solitude and repose from the rest of the world, where you can regain peace and mental clarity. If a noisy neighbour is preventing you from achieving such things on a daily basis, you might feel helpless, but luckily you're not. There truly are a several actions you can take to get your neighbour to lower the volume of his household. Writing a formal letter to this neighbour is one of those steps and a definitive way to make a gracious first approach to your neighbour.
Type your address in three to four lines at the top left corner of your computer screen. Skip a line and type the date. Skip another line and type your neighbour's address in three or four lines. This does more than simply establish the proper business letter format, it also establishes that you and the recipient are indeed neighbours.
Skip a line and type "RE:" plus the reason you are writing. For example, a suitable subject heading might be "RE: Excessive noise from your household."
Skip another line and type "Dear Neighbor:" or "Dear Sir or Madame:" if you don't know your neighbour's name. Type "Dear (insert neighbour's name):" if you do know your neighbour's name.
Skip a line and introduce yourself as the recipient's neighbour. Tell her where you live in relation to her, and immediately state the reason you are writing: the level of noise coming from her household is acting as a great disturbance.
Skip a line and describe the previous occasions where you've politely asked your neighbour to tone down the noise to no avail. State the dates and times of all the disturbances, and describe the nature of the sounds you've heard.
Skip a line and state that if the level of noise doesn't stop, you will be forced to call the police in the future or take action with a lawsuit. Skip a line and type "Signed," and then type and sign your name underneath, formatting these final words to the left.