Well, this is a good question to think through. Firstly, the original title uses alliteration with the repetition of the two "t"s in the "Tell-Tale". However, more importantly than this, I think Poe chose to name this story "The Tell-Tale Heart" because it is the heart of the man who was killed that forces the murderer to expose himself. To me, the last paragraph is key, as it appears as if the narrator has gotten away with it without any problems - the police seemed convinced that he had nothing to do with it. However, the narrator feels that he hears the heart beating again where he has stowed the body. This has an incredible effect on him:
Oh God! what could I do? I foamed - I raved - I swore! I swung the chair upon which I had been sitting, and grated it upon the boards, but the noise arose over all and continually increased. It grew louder - louder - louder!
It is this continual and ever-louder volume of the heart that literally forces the narrator to tell his tale and confess his guilt to the policemen.
i think it can represent the heart of the old man or the narrator himself..0kay!let say the tittle represents the narrator's heart,,when the narrator gets nervous when he hears a sound such as a watch makes when enveloped in cotton..actually i think the sound represents the heartbeat of the narrator who actually feel guilty.. maybe a little bit guilty,,in the nutshell,the sound of the beating heart symbolizes or actually is a metaphor for the guilt..the end
p/s: just my opinion about the story and the relation with tittle..i am not sure whether its true or not...peace...,,,,