The mention of the narrator’s sharpened sense of hearing in paragraph 1 hints at the old man’s death primarily because it suggests the narrator's heightened awareness of the old man's heartbeat. This amplifies the tension and foreshadows the moment when the narrator becomes overwhelmed by the sound and subsequently decides to kill the old man. Therefore, the most fitting response would be:
It hints at the point when the old man’s heartbeat drives the narrator to kill him.