Abstract: This paper took the self-ventilated permanent magnet synchronous motor (SVPMSM) as the research object. Experimental noise tests first identified aerodynamic noise as the primary noise source. Subsequent sound quality analysis revealed that adding a cooling fan, the loudness at a rotational speed exceeding 2000 r/min and the sharpness at a speed exceeding 4500 r/min both increased significantly, while the roughness decreased. To optimize aerodynamic noise, an expansion chamber was designed and installed in the ventilation duct. Post-optimization measurements show that loudness and sharpness were significantly reduced at nearly all test points, while the improvement effect of roughness was not obvious enough at a rotational speed of 4250 r/min. The sound quality test and optimization indicated that aerodynamic noise in SVPMSMs had a stronger correlation with loudness and sharpness. The results provided valuable insights for improving sound quality through aerodynamic noise control in duct design.