To me, the beating heart in "The Tell-Tale Heart" symbolizes the murderer's conscience and/or his guilt. It seems as though this man knows that he has committed a horrible crime and the guilt is literally destroying him, eating him up inside like a living creature fighting its way out. Though a manifestation of his mind,the beating heart is real enough to him to drive him to the verge of insanity and to an admission to the crime.
the noise symbolizes the guilt of the man who killed the poor elderly man.
It symbolizes his guilt for what he did to the old man.