In vehicle development, reducing noise is a major concern to ensure passenger comfort. As electric vehicles become more common and engine and vibration noises improve, the aerodynamic noise generated around the vehicle becomes relatively more noticeable. In particular, the fluctuating wind noise, which is affected by turbulence in the atmosphere, gusts of wind, and wake caused by the vehicle in front, can make passengers feel uncomfortable. However, the cause of the fluctuating wind noise has not been fully understood, and a solution has not yet been found. The reason for this is that fluctuating wind noise cannot be quantitatively evaluated using common noise evaluation methods such as FFT and STFT. In addition, previous studies have relied on road tests, which do not provide reproducible conditions due to changing atmospheric conditions. To address this issue, automobile manufacturers are developing devices to generate turbulence in wind tunnels. However, in wind tunnels, it is difficult to reproduce the large length-scale fluctuations of natural winds, and it could not sufficiently simulate the road conditions. In this study, we simulated the fluctuating wind that vehicles experience on the road and verified the fluctuating aerodynamic noise. We first reproduced wind noise under steady flow conditions and confirmed that the pressure fluctuation measured on the side window matched well with wind tunnel results up to 2 kHz. Furthermore, it was confirmed that using modulation power spectrum analysis, it is possible to quantitatively evaluate the fluctuating wind noise compared with FFT and STFT. From these results, we found that fluctuating wind noise is an acoustic phenomenon in which the aerodynamic noise generated around the vehicle is amplitude-modulated by fluctuations in the mainstream velocity. The technical challenge is to understand the separation flow around the A-pillar and side mirror, which generates fluctuating wind noise.