As someone that can hear a lot of "ultrasonic" frequencies, I would not assume it would be quiet. Those ultrasonic occupancy sensors are TERRIBLE. Your "quiet" laptop might be worse since the sound would be continuous instead of loud bursts.
You are correct. LTT's coverage mentions that while it's not loud, it's a bit unpleasant due to high frequencies. Although things might get tweaked with case design probably. Regardless, I am super excited about this tech.
After decades of jokes about laptops "lifting off" when under load, they will finally sound like a proper jet airplane.
I really wonder about what the impact of having a lot of these devices in a house with animals which can hear higher frequency ranges would be. Most (all?) rodents, cats, and--to a lesser extent--dogs all hear well into the ultrasonic range. I don't know if this is the sort of ambient noise that they'd habituate to easily or if it would cause constant stress.