Mufflers are used in the exhaust system for noise silencing, however, in the case of large mass-flow rate through the muffler, flow noise is generated in the stage of fast acceleration especially for Luxury vehicles such as Sedan. The complex flow fluctuations in the muffler cause this noise; however, the study of flow field in the muffler as well as the flow noise generated is in the beginning stage. In this paper, we have studied the detailed flow filed and tried to establish an analyses procedure for flow noise phenomenon. The steady and unsteady flow field was calculated by a commercial CFD code, SC Tetra V6. Flow noise generated from the muffler was calculated by acoustic analogy of Ffowcs-Williams and Hawkings. The strong fluctuation of pressure inside the muffler generates the strong broadband noise and we have validated the flow noise generation problem in the muffler with experimental data. Flow noise is generated as a broadband noise from 1000 to 4000Hz frequency range. Our analysis is found to be effective in finding the noise source location and strength as well in finding the noise generation mechanism.