What is making the rubbing sound in my trucks rear-end?

2005 Ford Escape. Since having brake pads and rotors replaced about a month ago, I can hear a loud "rubbing" noise from the rear end when braking or going slow. This seems to only happen when first driving after the truck as sat idle for a few hours, and after driving a short distance seems to go away. I took it back to where the brake work was done, but they said everything looks good and calipers are all working and rotors don't look out of round. Any ideas?