Interior permanent magnet (IPM) machines are subject to rich harmonics of air-gap magnetic field, which correspond to electromagnetic forces and resulting noise, vibration, and harshness (NVH) issues. In this paper, the NVH issue is evaluated based on a 160 kW IPM motor with focus on zeroth-mode vibration led by radial forces. Based on FEA, the leading radial force harmonics are analyzed and effectively reduced by rotor notching and asymmetric stator slotting techniques. Harmonic response analysis is conducted to verify the radial force optimization results. The results show 97.0% and 54.7% amplitude reduction on 48th temporal harmonic of total radial force for open-circuit and on-load operation, respectively. This corresponds to a 4.8 dB equivalent radiated power level (ERPL) reduction at on-load operation. The optimization approach is found effective in alleviating vibration issues of IPM traction motors without sacrificing output torque capability and will be validated by following-up prototype tests.