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As the chair enters the terminal the loud clunk with the long slow rumble that fades is the grip roller contacting the ramp that pushes the springs that open the grip. This takes plenty of force hence the loud clunk. This sound is slightly out of sequence with chair movement because of distance away from the source the video is being recorded and also because the sound has a tendency to reverberate inside the terminal.
The same sound sequence but at a lower volume is the chair leaving the terminal - just a reverse sequence.
The constant background sound is a combination of gearbox, electric motor hum and a dash of accelerator in the mix.

Also there is a slight rhythmic pulse to the whole mixture. This is caused by the electronic drive control constantly searching to find the right torque (power to the electric motor) and the "float" of everything mechanical in the drive system. The dynamics of pulling the haul rope up the hill are quite elastic. An experienced lift mechanic can actually feel this while standing in most drive terminals. An example would be driving a car on a level road and lifting the gas petal until the car just starts to decelerate then giving it a small amount of gas to maintain speed. The pulse or "wandering float" will gradually fade as the load increases.

Also quite noticeable from your video is the "pitch-back" of the bull wheel. This provides room for the accelerators and for the conveying system to go around the bull wheel without taking up to much room.