am i going crazy?

am i really going crazy. i was somewhat cleaning the house to try to keep busy. i was in our bedroom when i distinctly heard kelsey's piano. it was only one note. the cat is not here. im all alone. it was an F note closest to middle C (i went back to the piano and searched for the key i heard). it was clear and distinct. can that just happen? are there some sort of outside forces at play here? or am i going crazy? i know what i heard. i need to leave for a while im getting the creeps.