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Generation mechanism of transmission gear whine varies significantly by gear position, frequency and path/amplifier of the total system. Although controlling the source, namely transmission error/dynamic meshing force of the gears is desirable; it is not always feasible as well as most effective. This paper describes the root cause analyses of high frequency gear whine (overdrive position) of commercial vehicle, which combined in-depth experimental and CAE analyses. The generation mechanism of the gear whine is clarified efficiently utilizing Ford Spin-Torsional AWD NVH Test Facility, state-of-the-art Powertrain NVH development test cell, combining vehicle and sub-system NVH measurement. The analyses results showed the O/D gear whine is driveshaft airborne, due to alignment of driveshaft higher bending resonance to air-borne mode (“breathing mode”).