Q: Whining from transmission to rear end area 2007 Chevrolet Silverado 1500

I've had a whining sound accumulate over the past year or so in the transmission to rear end area. The transmission shifts smoothly up and down. However, i do randomly hear a light growl noise when the transmission downshifts, but its not bad at all. I've done some simple test to try and isolate the issue, but I'm second guessing myself. I've gotten the truck up to 50+mph while it whines, and taken the truck out of Overdrive into Nuetral, and the whine goes away. The whine comes back once placed back into Overdrive gear. I recently replaced the rear end differential ring gear bearings because I spun one. The whining started prior to the rear end bearing issue though, but I'm not ruling out the pinion bearing because I did not change it out. Is it possible that the whining goes away when I take it out of gear because there is no torque being applied to the read differential (if this is a rear end issue)?

Thank you, Blake Tumlinson

My car has 175000 miles.
My car has an automatic transmission.