My rear brakes developed a squeal when the brake pedal was released. My dealer replaced the rear brakes & disks at about 57000 miles. I had taken a salesman from the dealer to get an appraisal & he told me that it sounded like a simple adjustment would fix it. 2005 Elantra
When old brakes develop a squeal, it usually means that they have gotten too hot and the hardness of the pad has changed.
When new pads squeal, it usually means that they are supposed to have Teflon cushions behind them or they are supposed to have the back of the pads coated with a grease or other product that cushions the pad and dampens vibration.
If the pads have not been damaged and they are installed with the appropriate anti-squeal product for the application, and they still squeak, it is time to try a different brand or model of pad.