Apartments
A quiet walking pad is mostly a floor problem. The motor hum is secondary to the thud of each step on a hollow apartment floor.
Footfall travels through the deck into the subfloor. Neighbors hear that more than they hear the belt. Put the walking pad on a mat, keep speed in a walk, and avoid a jog setting this kind of machine was not built for.
If the walking pad is only used in the evening, storage matters as much as decibels. The C2 folds. A permanent under-desk treadmill stays in the room and gets used more on workdays, which can mean more hours of noise.
Hard floor, not carpet, if the belt is to track straight. Mat under the deck. Desk against an interior wall rather than a neighbor’s bedroom wall. Shoes with a soft sole, or the socks the manual allows.
Back to the best walking pads table, or the best under-desk treadmill if the machine stays out all day.