Answer:
Noise.
Explanation:
As per the given description, the professor is hoping the 'noise' aspect of the classroom to be changed as he seems quite distressed with the noise and clatter spread in the class which is not only disrupting the atmosphere of the class but also spoiling the message of the lectures' that he wishes to convey to them. He needs disciplined and peaceful surroundings to convey his message effectively to the students and thus, he hopes that this 'noisy' aspect of the class behavior must be controlled to promote learning and teaching constructively in the classroom.