A, as long as it interferes with people's normal study, work and rest, it belongs to noise, and the sound in a quiet library interferes with people's study, so it belongs to noise, so A's statement is correct and does not meet the meaning of the question;

B, the sound of the machine in the machine tool workshop is chaotic, which conforms to the concept of noise from the physical point of view; Therefore, B's statement is correct and does not meet the meaning of the question;

C, pleasant light music is also noise if it interferes with people's normal rest, study and work, or interferes with the sound that people want to hear; Therefore, C's statement is wrong; Conform to the meaning of the question;

D, the sound that interferes with people's normal study, work and rest belongs to noise, so D's statement is correct and does not meet the meaning of the question.

So choose C.