2005 Subaru Forester rear break noise

Noises problem
2005 Subaru Forester All Wheel Drive Automatic 83,000 miles

the rear of my car is making a squealing/grinding noise. The noise is not consistant, but happens at a variety of times. Sometimes when I break, sometimes when I am on flat streaches, sometimes up hill, etc. I replaced the break pads about a month ago, but the noise is there