[DoctorBeaver]

Can I get all smug again now? Can I? Eh? Eh?

[neilep (OP)]

Can I get all smug again now? Can I? Eh? Eh?

Ewe mean your smugness has an off switch ??

[techmind]

Thanks to ewe and all who helped unravel this.

Though, I would still like to know why this sound is made and what how is it made?

As you suggest, it is probably a "piezo motor" which does the lens-focus adjustment.
I don't know what sort of piezo motor they use for this application, but a few months ago we had a visit from the sales reps from PI come to visit at work and show off their wares...

http://www.physikinstrumente.com/en/products/piezo_motor/linear_motor_introduction.php
The animations they showed us were much clearer than the ones I can find on their website...

http://www.physikinstrumente.com/en/products/piezo_motor/piline.php
http://www.physikinstrumente.com/en/products/piezo_motor/nexline.php

Basically my understanding is that the motor in a camera might be more like the PI-Line version, where you have a small slab of piezo material (changes physical size when apply a high voltage) and you operate the motor by vibrating this slab (in the animation they showed us the whole thing quivers a bit like a jelly - but on a very small scale!) at resonance so its little 'tooth' or pawl "inches" the part to be moved along. The tip of the 'tooth' or pawl effectively moves in a circular kind of motion.

In contrast, the piezo-walk devices have pairs of legs which walk the moving part through, keeping it constantly under torque. These are more expensive.

[DoctorBeaver]

Can I get all smug again now? Can I? Eh? Eh?

Ewe mean your smugness has an off switch ??

No. Just an intensity control.