Toyota prerunner 4 cyl making funny noise when I shut off engine

New to the Tacoma...bought a 2013 4cyl with 40k miles. I notice when I shut the engine off, I hear a "whirring" sound in the engine..like fuel pump shutting off possibly?

 

Its an air pump that pumps air into exhaust or something like that. I don't know if v6 do it but all the later 4 bangers do. Its normal. My wife calls it the turbo.lol

 

My buddy calls it the Super Charger lol

 

OP, do you like or dislike the noise?

 

It's a good sound, it helped keep that engine passing emissions without bogging it down.

I actually disconnect them if I know I'm touching the exhaust and need to do major repairs immediately. They can increase the catalyst temp by 200degrees!

 

Ok. Good to know what it is!