Squealing Noise GTC4Lusso

I'm getting a squealing noise when off the brakes. It's been hard to discern a pattern. It seems most prevalent when I first start driving and typically goes away after getting up to speed for the first time. But it doesn't always happen. And lately it's started lasting longer into a drive.

This started when I got the car back from a new gearbox installation. Everything else in the car feels fine. I don't think the brakes were disassembled when the rear suspension was removed.

It sounds kind of like brake squeal, but louder and squeakier Perhaps a piston isn't retracting correctly?

What does the brain trust suggest? What should I look for?

Thanks!