Irritating screeching noise

I have a 2011 Kia SX. It has started making a screeching sound like nails in a chalkboard or some metal rubbing somewhere. Thought it was the brakes at first. Changed the front brakes totally. Checked the rear. One of the sliding pins was seized up pretty good but otherwise, brakes were in good shape. Thought it might be the drive shaft or u joints…mechanic checked and that’s all fine. Does it a lot slowing down and at first taking off, but will intermittently make the rubbing sound going down the road. At times more than others. Anyone have any clue what it could be?