Whistling sound at start up

I have an 08 2.7 with the five speed manual and for about the first minute after start up on a cold start there is a high pitched whistling sound coming from under the hood. I looked to see what it was and it's coming from a little motor by the the air cleaner that has a line going to the exhaust manifold..what is this contraption????

 

air injection pump. Sorry I don't know exactly how to explain it or why it's there, but I think it has something to do with lowering emissions.

 

Yup, air pump. By pumping air into the exhaust, it helps the cats warm up sooner.