Z Axis motor loud, gets hotter when idle

At first I noticed that moving my Z axis was much louder than the other two. I have my motors locked when idle, and the Z axis motor is about 10 degrees hotter than the other two. Is this normal?

Sound difference X/Y are connected to belts and Z is smaller belt + screw.
Heat difference is typical, anything below 170degF is considered safe as far as the stepper is concerned.

That’s kinda what I thought, although the heat difference is most prominent when the motors are idle.

And of course it never occurred to me that the noise difference could be because there’s a whole nother mechanism at work.

If reduced current limit is disabled ($1=255) then the stepper receive full power at all times, even when not moving. The coils are energized so the rotor stay locked to its magnetic detents.