If you were to dismantle the rear rotor and closely inspect the parking brake shoes (in the area of the operating lever) you will notice that the shoes may not be making contact with the anchor, or the stop. Reason: the slot in the shoe which accommodates the lever often is not deep enough, causing the shoes to rattle when driving over bumps/driveways. Try filing the slot a little deeper to allow the shoes to make full contact with the anchor/stop, than adjust the shoes as needed.
To my knowledge that brake assembly was/is not "self adjusting"
My .05's worth