Grinding Noise, Drivers Side Rear Brake Caliper?

[thatoneguy]

So for the past week I've been hearing a faint grinding noise when driving between 5mph-20mph, I hear it mainly in parking lots or stop lights.

I've had this problem before and it turned out a bolt from the front brake caliper fell out and the caliper was rubbing on the rotor, no damage, bought a replacement bolt and it's good as new.

Fast forward to this week. I started hearing that same noise I did with the front so my first thought is "great, another bolt fell out." I get home check the front calipers and there are no problems everything is dandy. I decide to check the rear calipers and the rear driver side caliper is loose.

All the bolts that hold the caliper in place are tight however you can still wiggle the caliper. The rear passenger side doesn't wiggle.

I for the life of me can't figure out why that is. I'm not sure if I need new brake pads, I've never changed the brake pads on the back and they don't look worn down to me Obviously that would be my first plan of attack and if that doesn't work maybe move on to the caliper.

Any thoughts? Suggestions?