Strange Noise at Start?

Couldn't figure out any way to search for possible answer already posted?

Every once in a while--its happened maybe 5 times in 5 months...at initial Start in the morning (car is garaged)...maybe cold, < 50 F, maybe not...hasn't happened for some time now and weather is now much warmer (Central Oregon)...

I hear a noise forward of the driver rather then rear of driver...either when pressing brake pedal before pressing Start or maybe not until Start is pressed too. I think the sound is mechanical but might be an electrical "buzz" that lasts for about 1 second only and stops and does not repeat. Thinking of something out of position that might move to reset to some nominal position? I then start driving and everything seems normal. Maybe something with a brake? I am not talking about the sounds that go on when the door opens which occurs every time. Nor the actual brake sounds. What I'm hearing is not normal but it also may not be of any concern either.

Any ideas? I'm going to try to describe this to a Prius tech but if any of this makes any sense someone here might go right to the problem--or it may be impossible. Thank you.

 

Yes I could but sadly, since I cannot cause the "rrrrrr" sound to occur, I don't see myself videoing starting the car every morning in the hopes of catching the sound. It must have something to do with something that runs for about 1 second when I initially push the brake pedal and/or the start button in the morning. In fact, my timing to post this is really to late because the noise is now a couple weeks overdue. I'm waiting to refine more exactly when during Start this occurs. I have cycled through all the air vent positions to no avail.

 

I just spent some time listening to and identifying all the sounds you have detailed above during Start but none describe the noise I very infrequently have heard. It is important to understand that this ~1 second noise is different from all the normal noises that clearly occur every time. I do notice now though that the air moving vanes/controls do "resettle" themselves (or it sounds like they do) after starting. I'm wondering if on occasion whatever this control device is it sticks making this "rrrrrr" noise I describe? I've cycled though all positions I can find though manually and none produce the trouble.

It's possible there could be some trouble code. How many weeks/months back are these codes held for? If an air vent control/actuator had some difficulty would something like it produce a code?

 

Would like to describe this ~1 second sound as an electric motor or solenoid "growling" maybe. Anyone know how easy it is to get to/examine the air/heat/cold vent actuators/solenoids? I suspect they are under the dashboard which would require disassembling the whole interior?