Squeaky noise in the rear coming from wheels are turning?

It sounds like you need rear brakes, here is how the job is done:

Rear Parking Brake Actuator Release - Service Mode
Prior to any rear disc brake or parking brake service, the parking brake actuator must be placed in Service Mode.

The brake fluid level in the master cylinder reservoir must be at 1/2 or lower to allow sufficient space for the fluid to return to the reservoir when the rear caliper retract is commanded.
Install a scan tool to the vehicle.
Turn the ignition ON with the engine OFF.
Release the parking brake.
On the scan tool menu, select Electronic Brake Control Module.
Select Control Functions.
Note: Do NOT apply any brake pedal pressure during this step.
Select Rear Brake Caliper Piston Retract.
After the repair is complete, calibrate the park brake. Park Brake Calibration
Rear Parking Brake Actuator Release - Manual Release
In the event the rear parking brake actuator fails or there is a loss of electrical power, the parking brake may be released manually.

The brake fluid level in the master cylinder reservoir must be at 1/2 or lower to allow sufficient space for the fluid to return to the reservoir when the rear caliper piston is retracted.
Remove the rear parking brake actuator. Rear Parking Brake Actuator Replacement
Insert an appropriate hex tool past the splines of the parking brake actuator piston apply spindle in the brake caliper.
Rotate the parking brake actuator piston apply spindle clockwise to release the parking brake.
After the repair is complete, calibrate the park brake. Park Brake Calibration

If the brakes are okay, it could be surface rust on the rotor in the morning. Can you please shoot a quick video with your phone so I can hear the noise? That way I can tell for sure what's going on.

Check out the images (below). Please let us know what happens.