Your neighbor has recently written to you to complain about the noise from your apartment.
Write a letter to him.
In your letter,

Explain the reasons for the noise.
Apologize.
Describe what action you would take.

Answer.

Dear Mr.Thomas,

I am writing this letter to apologize for the excessive noise which you noticed and intimated me. I am a resident of 457/12 South Kaloor, which is located next to the post office.

My eldest son ,who is a sound engineer,arrived home last Friday. As he has his final semester practical exam scheduled next month,he practises regularly. As a part of his trial, he went on making sounds of distinct frequencies till late night the whole week. I have never thought that the annoyance to the extreme. I really apologize for this inappropriate action.

As he would return to us by the next week, I can expect the same , and so, I am planning to make his room sound proof. I hope this would be the best solution for this problem.

Once again I would like to convey you my sincere apology.

I am looking forward to hearing from you.

Yours sincerely,
(Name)