Engine bay whine <2k rpm when cold at a stop

[Emil]

I normally don't drive it when < 50 degrees but it was 35 this morning. All was normal until I rev'd above about 5K and this whine started when the engine came back to idle and at a stop. It varied with rpm but pretty much went away after 2K or so. After driving on the xpressway for about 20 minutes it went away totally. Kinda sounded like a power steering pump but didn't vary when I turned the wheel. AC compressor maybe? It was pretty loud when it first happened. 96K miles. Any thoughts?
Thanks

 

[RichM1983]

Have you checked the idlers? They can squeal. Good luck!

 

[b_dike]

Are sure its coming from the engine? Have you considered the tob yet. Mine chirps at idle, but give it a few revs and the noise goes away.

 

[Buckwheat 1]

I had a sound similar to that.I had a vac leak from loose bolts on the super charger

 

[Emil]

Thanks for the suggestions guys!
I was pretty low on power steering fluid, under the min mark by about 1/2 inch, I topped it off.
It was directly related to engine rpm so I'm first looking at things driven by the belts.
It didn't happen on the way home so it may be one of those hard to replicate things.
I'll keep everyone posted.
Thanks again.