I have a 2006 Saturn Vue that has an intermittent problem. After commuting for 50 miles and parking for the day, when I leave to go home by pulling forward out of the parking space, there is a loud metallic clang and the left rear wheel locks. When I step on the brakes to stop the car stops, but the rear wheel stays locked. When I press the brake pedal all the way down about half way down there is a difference in pressure on the pedal and the rear wheel releases. This will repeat up to three times. Has also happened after the 50 mile drive and stopped at store for 20 minutes. Will not repeat every time, and of course not when there is a mechanic is anywhere near the vehicle.
Your rear brakes are drum-type brakes that have an internal mechanism that self-adjusts the position of the brake shoes as the shoes wear down from use. It sounds to me like self-adjusting mechanism may be broken or malfunctioning, causing the brake shoes to lock against the drum.
Take it to a trusted local mechanic (avoid brake chain stores if possible) and have them pull the wheel and drum off and check the brake mechanism. It should be pretty obvious to them what’s wrong.