There are two clips on each pad in the rear. 8 total, 4 per side of the car in the rear.
There is a spring tab on each clip that pushes the pad away from the rotor, when these break off you can have a squeal when backing up or have very fun sounds when the e-brake is engaging or disengaging.
I inspected my brakes over a week ago and found one of the spring tabs broke off so I ordered a replacement. When the rear brake caliper is apart you should be able to squeeze the pads in by hand against the rotors and when you release the pads should spring away from the rotors. If not you have a broken tab or really gummed up brakes.
If you attempt this please do the research. Secure the car(use chocks), use tow mode and pull the connectors apart on both rear brakes so you don't end up with a mess.