Brake pad/lining dust can often be the cause of brake squealing when brakes are applied. This is normally remedied by blowing dust out with compressed air.
If your rotors are warped or uneven, this will make a squealing sound. You may need to have your rotors turned or replaced.
I would check two things immediately...brake wear being the first, as most pads are now equipped with "sensors" that contact the spinning rotor to create a reminder squeal. Change the brakes at this point. Second thing would be brake dust as mentioned above, HOWEVER, it is not good practice to blow brake dust with anything. At this point, the rotors must be resurfaced to remove the "glaze" caused by heat and friction to their surfaces. Remember, when resurfacing rotors, or drums, replace all pads and shoes.
Answer
Some occasional squealing can be a normal characteristic on many vehicles. Also, if you tend to let the car sit without use for days at a time, learn to live with the squeal. A few drum brake systems (Neon rear drum brakes are of note) have a design that is inherently squeaky.
Disc brakes:
- Check for any of the following conditions:
- Corroded or pitted rotors; glazed rotor surface; grooved rotor surface; incorrect rotor diameter- can all be cured by resurfacing or replacement of rotor in combination with replacement of pads.
- Incorrect pads; hard pads; old pads; pads contaminated with oil or grease; inner and outer pads reversed; left and right pads. Replace pads to correct.
- Bent, out of place, missing, or corroded backing plates, pad shims or rattle clips. Correct as needed.
- Worn or loose wheel bearing.
- Design characteristic. Consider cutting reliefs into pads or coating the back (non-friction) side of pads with grease or spray-on tacky brake silencer.
Drum brakes:- Poor drum surface. Resurface or replace as needed.
- Cracked shoe linings. Replace.
- Shoes contaminated with grease, brake fluid, or gear oil. Replace.
- Weak return springs or shoe retainers, rusted springs, improper adjustment, lack of lubrication on backing plate at shoe contact points. Correct as needed.
- Inherent to design. Live with it. Also, consider coating the outside of the drum with high temperature enamel type paint. You will need to remove any rust from the drum and clean it with alcohol before applying. Sometimes affixing a spring or heavy band of rubber around the diameter of the drum can alleviate squeak.
If you're using low quality brake pads switch to a better grade.