Whirring noise from back

Just started noticing a whirring noise coming from the rear end. (or at least it sounds like it’s coming from the rear from inside).

These are the isolated characteristics of the noise.
-pressing the accelerator, even a tiny bit, makes the whirring noise. I can pulse the gas pedal super lightly and hear the whirring noise go in and out.
-going through gears does not influence the whirring tone or volume but the tone does gradually increase with respect to the speed of the car as long as the accelerator is still pushed.
-letting off the accelerator the higher whirring goes away but a lower sound is still audible.
-if you throw it into neutral, the noise completely goes away
-while coasting slowly down hill in gear(5mph), it almost sounds like bad wheel bearings.
-but again if you throw the car in neutral, the noise goes away.
-changed carrier(differential) fluid and added LS additive. Oil was very dirty but the change made no difference.

no other discernible noises like clunks or rattles.

Going to change transfer case oil tomorrow. Anyone else ever run into this? Bad pinion bearing? I read about bad carriers on these cars.

2014 CTS 2.0T AWD 57k miles

I’d guess you are hearing differential noise. Most diffs make some noise. Some are worse than others. Some can go a very long time making noise. Some can’t.

Have the pinon checked for movement and roughness. Either would indicate a failing pinion bearing. Same for the carrier bearings. On a lift or jackstands you can rotate the axles and pinion by hand to feel for roughness in the bearings.

If things are failing, they will get worse.

Thanks for the tips. I’m going to get it lifted and spin the rear to see if I feel anything back there.