To reduce the low frequency noise, a new method in optimal stiffener design is presented in this paper. A Microstructure-based Design Domain Method is employed to formulate a topology optimization problem. Using the MDDM, sensitivity of coupled system can be easily derived. The optimal stiffener design is solved using a sequential convex approximation method called Generalized Convex Approximation (GCA). Examples from this approach are presented to demonstrate its effectiveness.