Brake Related Question

Recently did a brake change on my 14 Q50S AWD, pads and rotors (Akebono) for front and rear for regular maintenance. After the change I did the same break in technique I’ve done with all of my vehicles and all was well. (This is my 4th VQ, 3rd with akebonos)

After letting the car sit over the holidays, I drove it today and as I put the car in reverse to back out, I immediately noticed a terrible screeching noise from the right side of the car. Stopped in the driveway, got out and inspected and all looked normal so chalked it up to new brake noises and kept on with my day.

After 30 minutes of driving, I noticed the car started to have a rotational noise, almost like something was grinding metal on metal. Pulled over and inspected both right side calipers, pads, rotors, and dust shield to the best of my ability, but again nothing abnormal.

Once home, jacked up the rear (I felt the noise was more from the rear but I guess what not positive) of the car pulled the caliper off and pads out, spent some time wire brushing any remaining gunk from where the pads sit in the caliper, re-greased, and reassembled. Upon test driving, still have the rotation grinding noise and the screech in reverse.

No weird pedal feel, no pulling, no vibration, car drives normal but sounds terrible.

What could this possibly be? I’ve done pads/rotors on akebonos several times without issue. What am I missing? Stuck pads? Failing caliper? Something else that’s going bad?

Anyone experience anything similar or have any ideas on where to go from here?