Noise at cold startup

[Xster]

There is a long "whizzing" noise coming from an "air pump" right next to the hood positive terminal for jumping on my 97 328i. The noise would last for approximately 2-3 minutes at cold startup then stop completely. What is that pump or whatever that is called? Any help would be greatly appreciated. Thanks,

John

[al_r]

That is your secondary air pump, 'injects' fresh air into the exhaust manifold at start up time till the ECU shuts it off - strictly emissions related. If the pump fails, you'll get a CEL/code indicating 'not enough volume' in the front or rear engine banks.
If you decide to replace it, also replace the valve it feeds on the exhaust manifold.

[Xster]

Thanks for the response al_r.