I need help. Can anyone tell me what the problem might be when I turn on the air or heat in my 2000 Grand Prix and it makes a whirling sound. The unit still heats and cools but the noise is enough to make me drive without using it. I don't want to get ripped off at the mechanic so please help!

I think it would be your motor squeaking The fan inside the motor. Hopfully someone else will chime in
and give you a more diffinate answer

I agree with GTPWarrior the blower fan is you problem. You may need to replace the motor and the fan. I had a similar problem, changed the unit, quiet as a mouse. Only cost $25 from a wrecking yard and about an hour to change. Tough to get to!

Sounds to me that both "GTP's" are right. Had the same in the Wifes car. Pulled it and cleaned it. Works great.
http://img.photobucket.com/albums/v425/kustomkid54/1998PontiacGrandPrixGTP003.jpg