The correct option is
A that
As we can see, the answer will connect the first clause to the pronoun 'you'. This can only be done using relative pronouns and so the answer must be a relative pronoun. Further, it should refer to the 'sound' heard by the subject.
Option A is correct. 'that' is a relative pronoun. It can refer to the 'sound' heard by the subject. Thus, it meets the required conditions and is the correct answer.
Option B is incorrect. 'what' is an interrogative pronoun and not a relative pronoun. Thus, it is incorrect.
Option C is incorrect. 'who' is a relative pronoun that is only used to refer to people. It cannot refer to something abstract like sound. Thus, it is incorrect.
Option D is incorrect. 'whose' is a relative pronoun that can only refer to people. Further, it indicates possession. Thus, it is used to indicate that something belongs to a person. It cannot refer to 'sound'. Thus, it is incorrect.