With abnormal noise usually occurs when braking of a hybrid power bus in mixed mode

time-frequency analysis is performed by using complex Morlet wavelet for a collected noise signal.Combined with filtering analysis and sound playback technology

the time-frequency information of abnormal noise is determined

the results show that the abnormal noise and vehicle speed are directly related.Extracting the abnormal noise frequency from the conditions varying initial braking velocity:39 km/h

48 km/h

56 km/h is the same as the frequency of bevel gear.It shows that the abnormal noise during the vehicle braking comes from the bevel gear.For the abnormal noise sources

measures of bevel gear matching carefully and shape modification are taken.Real car Subjective test shows the abnormal noise is decreased greatly

and sound level is improved effectively.