auto trans squealling noise in gear.

[GreenChevelleSS]

My SC400 has a squalling noise coming from the transmission while its in gear at idle and stopped. you can bring the revs up right off idle and it will go away. It sounds just like a belt and pulley squeal noise, I even thought it was till I left it in gear with the parking brake on and put it on our lift to verify.
Anyone have any recommendation or ideas what could cause this? Fluid looks good and right on. Transmission works great.

I also thought I heard the noise with the cruise set driving down the highway with the windows down but I could have just been hearing things.