The noise level and sound quality performance of a passenger vehicle are strongly dependent on the fluid-structure behavior that is the interaction between the air inside the cabin with its sheet metal structures. With the challenges of global platform vehicles and an increased ethanol usage as an alternative fuel, new approaches of product development and refinements become necessary in order to up-to-date standards of vehicle NVH (noise, vibration and harshness). By using a CAE model combined with experimental data, it was possible to predict the main noise and vibration propagation paths inside the vehicle, where some proposals could be handled in advance and then validated on vehicle. Several solutions may be found to solve issues that usually are delimited by technology, cost-benefit ratio, production ability, package restrictions and/or durability. This paper describes how to minimize harshness and as a consequence improve the sound quality inside a passenger vehicle with a flex fuel engine by using a passive mass damper applied into a transmission mount.