Or 5. the sound isn't related to turbolift movement as much as it is to the turbolift being inside the constantly humming network of shafts; the sound fades into the background when the doors are opened and ambient noises of another type drown it out.
Although I like the theory #2 best.
Perhaps the waiting area for bridge turbolifts is below Deck 2 (and this somehow relates to how turbolifts were unusable below Deck 3 specifically in ST2:TWoK), and Spock simply holding the lift would have caused undue traffic jams for that reason?
Or then the waiting area is on Deck 2, and the noise comes from all those other
lifts busily humming?