The mileage is about 20 thousand km, equipped with the CJTC engine and the 2013 Audi Q7 3.0T sports utility vehicle with OC8K-8 automatic transmission. User reflection: the rear of the car has a different noise. Inspection and analysis: the maintenance personnel test the car, found that in the back seat near the car can hear a more obvious and regular "Da Da" sound, similar to the carbon tank electromagnetic valve when the sound of the work. When the carbon tank solenoid valve works, it will produce intermittent switch action sound, but the sound actually heard is not coming out of the carbon tank solenoid valve on the upper right rear wheel. Detection of engine control unit, found no fault code, indicating that the cause of abnormal sound in mechanical aspects. The engine, the transmission, the chassis and the body are all mechanically connected. When a certain component gives out a different sound, it is transmitted by other components, which brings difficulty to the fault location. The failure point is likely to be the loosening of the components of the above systems. The lifting vehicle was monitored by stethoscope and it was found that the sound was more pronounced in the fuel tank area. Inspection found that the fuel pump on the fuel pipe is not fixed, touching the fuel tank wall, causing abnormal noise. Troubleshooting: fixing the fault location, checking the vehicle after maintenance, eliminating the abnormal sound and eliminating the trouble.