In the end, the narrator murders the old man and confesses the truth to the policemen after hearing a ticking noise that seems to be coming from the old man's dead heart. I would keep the ending the way it is because although the narrator thinks that the sound is coming from the old man's heart, it is really the rapid heartbeat of his own guilt. This ending is important because it what makes the title of the story "The Tell-Tale Heart".

Part 2.