Troubleshooting and diagnosis are proceeded for an abnormal noise problem of a vehicle with a turbocharged gasoline engine at accelerating condition. The frequency band of the abnormal noise is 320~470Hz. In order to get the time-frequency characteristics and sound source of the abnormal noise, tests of basic sound, vibration, sound intensity and combustion are proceeded. The experimental results reveal that the abnormal noise is radiated from every engine surface and has little connection with the combustion. Thus the crankshaft vibration is suspected to be the main cause of the abnormal noise. The torsional vibration tests of the crankshaft with different torsional vibration dampers (TVD) are executed, the time-frequency contour maps of the torsional angle have similar characteristics with the abnormal noise, affirming the former suspect. The simulation of the crankshaft torsional vibration is proceeded in order to find an optimum TVD, which is verified as the best vibration absorbing effect at 350 kHz. Then the optimized TVD is manufactured and tested, the indoor noise shows that the amplitude of 320~470 Hz is attenuated dramatically and the abnormal noise is eliminated successfully.