1997 Chevy Suburban Whining transmission

Transmission whines until it shifts out of 1st gear. Seems to shift at normal rpm's and doesn't seem to shift hard. Whines till it shifts out of first and then whines slightly after I reach desired top speed (60 mph) and let off accelerator slightly. If I give it more accelerator, the whining stops until I let off the accelerator again. Its not very noisy at 60 mph but, in 1st gear its pretty noisy. I just noticed this problem since the weather warmed up and i've been driving with the windows rolled down. I'm not really sure how long it's been making this noise since I usually have the radio on. I noticed it about a week ago, but may have been doing it longer.