Meaning: This sentence personifies the piano keys, suggesting that they have a voice and are communicating something intimate and meaningful through their sound.
Choice of Words: Piano keys are the individual keys on a piano that are pressed to produce sound. "Whispered" is used to describe the soft, gentle sound that the keys make when they are pressed. "Secrets" suggests that the music played on the piano is private and personal, as if it is sharing a secret with the listener.