Abstract: In recent times, rear spoiler wind noise has garnered significant attention. However, the lack of understanding of its mechanism has prevented the development of effective noise reduction methods. To address this issue, we conducted a study on its mechanism with the aim to reduce its influence on the interior noise. Using the lattice Boltzmann method (LBM), we simulated the compressible and unsteady flow fields around a vehicle. Statistical energy analysis was then used to obtain the interior noise, which was validated by wind tunnel tests. Next, to locate the noise source, we employed the wave number analysis method to decompose the pressure at the glass surface into the turbulent and acoustic parts. The results indicate that the low-frequency spectrum peak of the interior noise is primarily attributed to the sound pressure induced by periodic vortex shedding and the fluctuating turbulent pressure by the interaction between vortices and glass surface. The high-frequency spectrum peak is mainly due to the radiated acoustic pressure generated by high-speed air flows. Finally, we proposed an optimized rear spoiler which can reduce the low- and high-frequency spectrum peaks of the interior noise by 5.5 dB(A) and 14 dB(A), respectively. This optimized design offers a promising solution to reduce wind noise and enhance driving comfort.