The thesis project is the description of the optimization process with the aim of improving the vibrational performance of a rear axle differential of a high performance vehicle whose main cause of emission is the bevel gear set. The same group is fitted to different car models but only in a couple of these are heard a whistle during a certain working condition. This condition required an optimization of the differential design from the NVH point of view. Therefore it is wanted to investigate in depth what are the parameters that influence this behavior, starting from the analysis of the macro and micro geometry and continuing with the analysis of other components such as bearings, shafts and housing.