Air pump is under the alt.

Air pump bearing goes south and makes noise on start up , when it is used.

You can disconect the air pump and start the car. If there is no noise then there is your problem.

Follow the wiring harness from the air pump, above the alt, and behind the front (black) cover. You take the cover off, then reach back and disconect the harness.

Start the car up and see if the sound goes away.

Let us know the results to help future people with this problem.