Sound from air vents when AC first turned on

The Prius uses electric motors to position the baffles in the A/C system. I suspect this is what you hear.

Tom

 

pctra,

At least in the Gen II, the soft whirring and door closing sounds on
start up of the air conditioning -- meaning either heating or cooling
-- comes from the servo motors setting baffles in the ductwork to
direct air as as desired. I hear it when I change output location, say
from defrost to feet & face. I would say that unless the sounds are
very loud, or sound particularly strained, there is litttle to worry
about.

I suspect that the Gen III is pretty much the same.

One caveat: If you live in a rural/suburban area, be mindful that
mice and chipmunks have a particular fondness for setting up
houskeeping in a Prius' ductwork. So a loud or strained sound could
mean a stuck baffle due nesting, etc.

But just in case, let's wait and see if a Gen III-er chimes in.

Hope this helps.

 

It could also be the compressor when it first turns on.