I always wondered, what is that whirring/revving/priming sound when you put the key into accessory mode before starting the car after sitting for a night or a long while?

My car has done this ever since I got it 4 years ago, now it just stopped lol

Car drives fine btw, starts up and goes.

RX-8 hypochondriacs unite!

 

air pump?

 

Throttle body going through its initial test.