Whistling Sound accompanied by rough idle

[TheJMan]

About 2 weeks ago, I replaced my alternator trying to get rid of this terrible whistling sound coming from under the hood. That did nothing and the sound is getting louder day by day. It only whistles and squeaks when cold. The sound seems to be coming from around the alternator area but the new alternator didn't fix it. Could it be a sign of a bad idler pulley or IAC?

 

[jimbo74]

could be either of those..... i think my dads iac is going, and read about it here, let it idle and disconnect it, if its damaged, it should run poorly or die..... also i have heard if it is the iac it will only make noise at idle

 

[TheJMan]

It idles ok, but not great. The RPMs will fluctuate up and down about 100 rpms, sometimes dipping down to about 400 and the whole truck shakes.