The Auxiliary Power Unit (APU) is a widely used onboard device in civil aircraft and is considered one of the sources of cabin noise. Understanding the relationship between APU vibrations and the cabin noise helps in designing better vibration isolation systems. This paper presents tests conducted on the APU vibration and cabin noise under different operating conditions for a tail-mounted engine civil aircraft. The results indicate that when the APU generator is operating, there is a significant increase in vibration energy at the generator rotor frequency. Additionally, when the APU provides bleed air, the vibration energy at the APU rotor frequency also increases. The highest average sound pressure level in the rear cabin was observed when the APU was simultaneously generating power and providing bleed air. There is a strong correlation between the cabin noise sound pressure levels at the APU generator frequency and rotor frequency and the vibration energy of the APU itself. Specifically, during APU electrical power generation, the vibration energy at the generator rotor frequency significantly increases, leading to a marked increase in the cabin sound pressure level at that frequency. Therefore, when designing the APU vibration isolation system, it is important to focus on effectively reducing the transmission of vibrations and noise from the APU generator and APU main shaft rotor frequencies.