Shape and topology optimization analysis using a homogenization method has received much attention because it can treat topological changes of a design domain. However, as far as dynamic problems are concerned, it has not been successfully applied until recently. Here, it is applied to the reduction of interior noise in the coupled structural--acoustic system for the first time. Attempts were made to reduce the mean eigenvalue formulated by Ma et al. and the sound-pressure level integral formulated by Kozukue et al. by using a homogenization method, and the validity of these combined methods is demonstrated.