Humming coming from under the hood

Found an old posting from a few years ago by a board member but never received a response back from him so I thought I'd repost it because it is the IDENTICAL situation I am having. From what i can tell it only happens when i first start the car after it has been sitting for a while. i start the car and when it comes down to idle (~750rpm) there is a noticible "howling" sound comming from the front of the car. i opened the hood and poked around, but couldnt see anything out of place. sound SEEMS to be comming from the drivers side of the engine near/at the front. does not matter if the lights, radio, or ac is on at the time. also does not go away when i depress the clutch or brake. if i play with the gas it will go away once i get the RPMs passed 1500, then return once it goes below that point. after i run it for a bit it goes away entirely even at idle. if you turn it off and start it back up it is still gone.

this howling sound has seemed to get a bit worse and is now starting to draw my attention more often. the best way to describe the sound is if you take a larger margaritta glass, put lime around the outside, then run your finger around the edge to get that "harmonic vibration" sound. I'm realy lost on this one.... any ideas?

Some have suggested that it MIGHT be the idler pulley getting ready to seize. Another suggestion was that it could be the idle air control valve. Any other suggestions?

Thanks in advance!

Jared

Oh, I have a 2003 V6 'Stang (no engine mods at all - everything stock).

Thanks for the replies. I should also mention that it only does this humming once the engine is warm.

I will look into the idle air control and the plenum. I don't believe it'd be the power steering pump, as there's no change in the sound when the wheel is turned.

I'll repost once I can get to it. It may take a few weeks with christmas and all barking at the door. ;-)

J