The AC noise of motor capacitor comes into being through the vibration caused by MPP′s static force and electromagnetic force.The AC noise consists of harmonics which is of integral times of the frequency of the voltage applied.The noise which takes main action to human′s ears is the harmonic wave with 1000Hz.The low temperature aggregation solved AC noise would affect the capacitor life.The AC noise will not affect capacitor′s other performances.Mucilaginous polyisobutylene can absorb AC noise.