Metal dragging/nails on chalkboard noise

I drive a 2008 Kia Sportage. After driving for about ten minutes I noticed a noise that sounded like something was being dragged along the ground under the car. It stopped when I braked and does not happen when I turn corners. I checked under the vehicle and nothing appears to be dragging. After having a break the car did not make the noise again until is had driven for about 5 minutes, again the metal dragging noise, noise goes away when braking and turning. Car was in for service last month and was told brakes looked fine, what could this be?