Tranny whinning on 1999

Just bought a used 99 Ranger had an older model with a standard transmission that seemed quiet, compared to the newer model.
When idling and the automatic transmission engaged there is no noise as I pick up speed the noise increases. Is there an additive that I can add to the transmissionto quiet this noise.
Is the noise coming from the transmission or is it coming from the rear end. Any thoughts, need help.

Try changing the transmission fluid. Sounds like it might have the wrong fluid in it. I have a 4.0 5spd. I had the rear seal replaced on the transmission and they put the wrong fluid back in it. Two weeks later the transmission started whinning. Took it back in and they said it was the rear end. Two days later the transmission came apart at about 80mph. The main bearing came loose and basically the truck went into reverse at 80mph. The shop of course claimed the put the right fluid back in but it was clearly gear lube in it.

Going to try to replace tranny oil and filter next week have already replaced rear end fluid, thinking that the noise was coming from the rear end. If it isn't the tranny it might be the drive shaft. Has anyone had problems with the drive shafts not balanced in this model and year of truck. please reply, need help.