Transmission whining, maybe?

Hello there my name is matt ive been listening to your show forever and ive always wanted to submit a question and now i think i have a pretty good one. I just recently purchased a 1992 gmc sierra.The motor has about 40k on it and the transmission was apparently rebuilt at some point and has about 75k on it. Everything runs great with the truck except that everytime im in gear and i hit the gas it makes a loud whining noise that kinda fluxuates with the changing of the gears. Its an automatic by the way. You can hear the sound speeding up and getting louder as i give it gas but when i let off the gas no matter what gear im in the noise stops completely. If there is anything you can suggest i would greatly appreciate it. Thank you so much!

Pump and/or torque converter. It has to come out. I would let a trans shop take a quick look.