I was terribly sorry to receive your letter complaining about the noise brought from my flat last Friday night
I was terribly sorry to learn about the noise created by us that disturbed the neighborhood on the night of last Friday.Please allow me to explain a little that we threw a welcome party for my sister who was just back from Australia after 4 years studying abroad.
While I acknowledge our fault and accept the responsibility of this inappropriate conduct, I humbly request you to allow me to explain why this incident occurred that night.Good writing & good luck! :)