Grinding noise

I have a 14 tundra sr with 80000 miles I’m a new owner I’ve had trucks in the past. Noticed grinding noise after parking brake has been applied for a long time. I released it and drove like normal and got horrible grinding noises for 30 min. Not too sure I’m certain it is not the bearings I was thinking could it be backing plate for parking brake or misadjusted parking brake/slide pin?

 

Maybe got rusty and sticking a bit?

 

Rocks, sand, or grit between pads and rotor. I was getting grinding, squealing sounds after I went wheeling. Popped the wheel off, removed two 17mm bolts, slid the caliper off, cleaned the surfaces, and then reversed the process. Noise gone.