In recent years, commercial vehicles with leaf suspension has been demanded to be as quiet as passenger vehicles. Therefore, rear differential gear whine noise also should be reduced and not to be stick out from interior back ground noise. It is known that the gear whine noise is strongly influenced by resonance of leaf suspension and the resonance frequency varies widely. This paper reports control method of the vibration characteristics of leaf suspension by changing the contact position and stiffness between each leaf, which is the main factor of variation. Using this method, gear whine noise could be decreased effectively.