I'd imagine you'd have to sedate the passenger? That would be far too scary and long a trip to risk them panicking when there is nothing you can do.
Better to take a chance on ordering the boys to lie there and DON'T MOVE!
Could also help to make them stay awake for a long time, then transport them - they'd likely fall asleep in the dark quiet.
And would it be quiet? I would expect sounds of air bubbles, breathing apparatus, scratching along rock in the tightest passages, etc. Nothing high-volume, but it would certainly be audible.