Inspection and analysis: the maintenance personnel found that the abnormal sound was easy to appear when the vehicle suddenly turned to speed up from the deceleration state. Repeated tests showed that the abnormal noise would occur when the driving force of vehicle suddenly changed. It can be seen that the fault is likely to be related to the load of the transmission shaft. In order to simulate the load change of the drive shaft, we should try to reverse the car quickly and then accelerate it forward. So that sound can appear every time. Judging from the outside of the car, the sound comes from the left rear axle. It is suspected that there is a loosening between the axle and the hub, but the failure after fastening the half axle nut is still. Conversely, when the half axle nut is loosened 1 times, the abnormal sound will disappear. This shows that the abnormal sound is caused by the slight displacement between the axle and the hub, and the friction noise generated by the movement is amplified by the parts and then transmitted out of the vehicle. Troubleshooting: apply the thread lock glue to the half shaft end and replace the half shaft nut. After loading, make sure that the fault is completely eliminated.