What you hear is the sound of the refrigeration system. This sound is a kind of noise, because after the compressor starts, the system pressure from the equilibrium state instantly changes to the high and low pressure difference state, resulting in a system pressure difference. About 3 minutes later, the system pressure tends to balance, the noise will disappear, it is recommended that you experience it again. At the same time, the compressor will have a normal high-frequency or low-frequency sound, which is a normal working phenomenon, please rest assured that the use.