Squeak/whine when coming off the brakes

Company car/van:  2023 Ram Promaster City, the little van.  

I got it new with just 400 miles.  Today it rolled 56k.  Also today I notice for the first time ever I am getting a consistent squeak sound when I come off the brake yet no noise when I apply the brake.  Sound like rear brakes.  Maybe right rear only. 

Sample:  Going from Park to Drive.  Apply the brakes to free the neutral safety switch and drop the car into drive.  When coming off the brake pedal there is a squeak but no squeak when applying the brakes.  Drive down the road and all is well as in smooth  driving at all speeds.  Come to a stop light and the brakes apply smoothly with no noise or feel.  Go to leave that stop light and thereby release the brakes and there is a squeak.  

Rears are drums.  Is this a wheel cylinder sound?  Would it make the sound only in one direction of it's movement?    

Yeah I think it's entirely plausible that there's only a squeak when releasing. So, does the squeak only happen when releasing from a stop, or if you decelerate to a non-zero speed then release the brake to continue does it squeak as well?

In any case, with 54k on it I'd clean everything up and throw some new shoes on and I bet it goes away.

Could it be a pneumatic noise from the brake booster perhaps? If you pump the brakes a bunch when parked does it squeak on every release? Any difference if you try with the engine off and vacuum depleted?

Shoes are squeaking against the backing plates.  A little black brake grease and it's fine.