A constant squealing form the brakes when driving, turning, or braking may be the sign that the brake pads are worn to a point they need to be replaced. Most disc brake pads have lining depth indicator. This is a metal tab that is contacts the rotor when the pad is worn down to a point that replacement is needed. If left unrepaired, this tab WILL damage the rotor, adding to the cost of repairs.
A squeak or squeal only when braking can also be this indicator tab, but may just be a condition common to semi-metallic pads. Brake squeal is typically caused by vibration between the brake pads, rotors, and brake calipers. Some brands of semi-metallic brakes are more likely to experience brake squeal due to the metallic ingredients in the brake pads. There are several products on the market to combat this annoying noise. This is assuming the brakes have been checked and there is no visible problem.
When installing new brake pads, it is important to use new mounting hardware. Most hardware is made from soft materials like rubber or spring steel, which are designed to insulate the pads and caliper from the mounting bracket and wheel spindle or hub.
Some of the cheaper, lower cost replacement brake pads have a tendency to squeal or squeak when they get hot. There is not a lot that can be done about this. It is just a characteristic of this kind of part. The anti - squeak lubes and pastes that you can buy at any parts store may help with this problem.