I see.
It is my understanding that the noise is non-intermittent and continues
even when the camera is placed on a tripod. Presumably this is some
kind of polling behavior. Why is it necessary and why does it make a
noise?
I think you'd have to ask a Canon engineer or someone who's had one to
pieces and run a bunch of tests - unfortunately I'm neither.
Speculating, I don't find it surprising that the actuator would always
be moving (and thus making noise) while the system is active. Any sensor
will produce some level of noise in its signal (in the electrical,
rather than accoustic sense), as will the electronics betwen the sensor
and actuator. This noise can be translated to small movements of the
actuators back and forth around the desired position. Damping that
noise, electronically or mechanically, would degrade the response of the
system to rapid changes. It's not unusual for control systems to
oscillate a little around their desired operating point, particularly if
they are optimised more for rapid response than minimum overshoot and
oscillation.
Tim