## 1 Introduction
According to their test results, noise levels significantly decreased under both gears, with the optimized noise peak value reduced by 5-10 dB. Studies have also been conducted on booming noise generated by parts of electric vehicles other than powertrains. [PERSON] and [PERSON] [23] explored the booming noise originating from the rear cross member due to road-induced vibrations and introduced methods to construct a model for system-level analysis. [PERSON] et al. [24] and [PERSON] [25] conducted respective studies on the tailgates of sedans and sport utility vehicles (SUVs), and [PERSON] et al. [26] conducted a similar study focusing on the noise generated from the roof and floor of hybrid vehicles. Various methods have been explored to reduce this booming noise. [PERSON] and [PERSON] elucidated the booming noise generation mechanism caused by the torsional mode of the rear cross member [23]. They applied topology optimization and multi-model optimization and developed a conceptual design, presenting concrete design proposals applicable to actual implementation and production. Acoustic metamaterials were incorporated based on the band gap theory into the finite-element analysis model of the vehicle's tailgate to diminish the booming noise arising from the thin sheet metal components of the tailgate [24]. A carefully designed approach incorporating resonators to decouple the interaction between the body modes and internal acoustics was proposed to reduce booming noise and was subsequently validated through experimental confirmation [25]. The internal noise distribution inside the vehicle was acquired to reduce the noise generated by vibrations on the roof and floor of the vehicle [26]. Materials equipped with damping and absorption capabilities were attached to the roof and floor of the vehicle to experimentally confirm their noise-reducing effects. [PERSON] et al. [27] eliminated road noise using active noise control through the application of an adaptive parallel filter method. Additionally, [PERSON] et al. [28] developed an equivalent sound quality model of the interior sound in electric vehicles, while [PERSON] et al. [29] carried out research on the evaluation method of the interior sound quality of electric vehicles. According to our investigation, most existing studies related to booming noise primarily focus on analyzing ICE vehicles, with broader research on electric vehicle NVH emerging only recently owing to the proliferation of electric cars. Nonetheless, few in stances in the existing research specifically address booming noise in electric vehicles, especially that related to tailgates. The aforementioned studies appear to cover the entirety of research conducted in this domain. As mentioned earlier, [PERSON] et al. [24] proposed noise reduction methods involving attaching acoustic metamaterials to the tailgate, whereas [PERSON] [25] studied the tailgate but faced limitations involving additional weight and cost owing to the use of dynamic absorbers. Instead of introducing extra components such as absorbers, modifying the design of the tailgate panel and adjusting the boundary conditions between the panel and vehicle chassis, thus improving the system itself, presents a more efficient solution to mitigate booming noise with relatively less time and expense. [PERSON] and [PERSON] [23] sought solutions by enhancing the cross-member itself rather than attaching it, exemplifying this strategy. To overcome these challenges, this study not only identified the causes of road-induced booming noise in electric cars but also proposed solutions by modifying the dynamic characteristics of the tailgate itself, eliminating the need for additional elements. Additionally, our research facilitated the investigation of booming noise by creating a finite-element model of the tailgate during the preliminary design stage, a step before the finalization of the entire model.