Avoiding quality problems in passenger cars, such as squeak and rattle (S&R), has been a remarkable cost-saving consideration. The introduction of electric engines and autonomous driving is expected to further stress the need for quieter cabins. However, the complexity of S&R events has obstructed the practical treatment of these quality issues in the pre-design-freeze phases of product development. In this study, new quantified frequency-domain metrics are proposed to measure the risk of S&R generation in car subsystems. The proposed metrics measure the resonance risk and the mode shape similarity in the critical interfaces for S&R. The calculations are done based on the system response in the frequency domain. Compared with the time-domain evaluation methods, the knowledge about the system excitation levels is not essential and the calculations are more time-efficient. The proposed metrics can be used in design optimization processes to involve S&R attributes in the pre-design-freeze attribute trade-off activities besides other attributes. In this work, these metrics were used in a previously developed two-stage optimization approach to determine the connection configuration in two industrial cases. As compared with the baseline design, the risk for S&R was reduced by improving the system behavior in terms of resonance risk and mode shape similarity. This was achieved by applying adjustments to the location of the fasteners while maintaining the same general connection configuration concept.