A, the site can't be carried out without large-scale mechanical operation, which does not conform to the meaning of the question;

B, it is unrealistic to isolate all noise sources in a vacuum container, which does not meet the meaning of the question;

C, planting trees and flowers around the campus can reduce the noise on the way of sound transmission, which is feasible and in line with the meaning of the question;

D, the sound source is produced by the vibration of the object, so it is impossible for the noise not to vibrate.

So choose C.