I have had this happened to me already 3 times, 2 on the right rear, and once on the left rear. I can tell you to change it as soon as possibly. I took out my calipers, and beat the rust off that had built inside. it runs good for a while till it happens again. My suggestion is to buy new calipers, pads, and rotors if need be. If cash is an issue, like my case, then just make sure to check the problem out and do a temp fix.
Now real quick, how and where can i repack my bearings?