Low-frequency road noise is a primary contributor to in-cabin noise and directly affects overall vehicle comfort. With the rapid development of electric vehicles, this issue has attracted increasing attention from the automotive industry. This study conducts an experimental investigation on the low-frequency noise contribution in a new energy multi-purpose vehicle(MPV) using the classical transfer path analysis (TPA) method. By integrating modal analysis and operational deflection shape (ODS) analysis, the noise-contributing components along the transmission path are identified. For the identified components, structural optimization is performed through simulation, including tailgate reinforcement and rigidity enhancement, aiming to increase modal frequencies and decouple problematic resonance frequencies. The effectiveness of the optimization is validated through vehicle testing. Test results indicate that the main contributing frequencies are 27 Hz and 43 Hz. The 27 Hz component arises from the X-direction rigid body mode of the rear suspension and the first-order rigid swing mode of the tailgate. After optimizing the tailgate structure, its modal frequency increased from 29.2 Hz to 32.9 Hz, resulting in a 4 dB(A) noise reduction in the front row and 6.4 dB(A) in the rear row. The 43 Hz component is mainly due to the first-order mode of the panoramic sunroof. By modifying its surface curvature, the modal frequency decreased from 37.8 Hz to 32.1 Hz, leading to noise reductions of 7 dB(A) in the front and 3 dB(A) in the rear. The proposed optimization strategies significantly improve interior noise performance and provide valuable references for low-frequency road noise control in vehicle design.