Reducing noise emissions from vibrating components in a vehicle's underhood environment has always been a priority at the OEM level. In recent years, it has been receiving a rather significant amount of attention due to the increased usage of plastics in the underhood environment. Due to it's lower mass density property (as compared to metallic materials), plastics have some general disadvantages in terms of acoustical insulating properties. Yet, the design of these parts can be changed so that the noise emissions from plastic components can be reduced to levels similar to metallic components by using advanced simulation techniques and optimizing the vibro-acoustical behavior of the part. The goal of the design engineer has changed from only traditional part design and structural or weight optimization to include acoustical optimization of the plastic underhood component. It is essential to the success of a program to simulate, evaluate, and optimize the acoustical performance of a vibrating part at an early stage of the development cycle before any prototype parts are produced. The purpose of this paper is to introduce methodologies to acoustically optimize the performance of a component using advanced CAE techniques. The subjects of optimization are typically air intake manifolds, engine covers, rocker covers, air filter housings, whole air induction systems, valve covers, and any other plastic components contributing to the noise radiation from the underhood environment.