Brake noise is always reason for concern. The three most common noises that a driver will hear are squealing, scraping, and grinding.
Squealing Sounds: Brake squealing is by far the most common of the problematic noises that you will encounter. Squealing noises can be nothing more sinister than dust and accumulated debris that has gathered on the pad, but it is normally indicative of a more serious brake problem. Squealing noises are most noticeable with semi-metallic brake pads because they involve metal rubbing against metal. The asbestos material in these pads has been replaced with metal shavings. Despite the high-pitched squealing noises, these brakes are functioning correctly. Because these semi-metallic pads tend to last longer and are frequently more superior regarding stopping power, manufacturers tend to ignore the noise problems associated with their functioning. Some of the genuine problem which cause this sound is a) Dust in the Drums: Dust created as brake shoes wear down tends to accumulate in the drums and creates a classic squealing sound. This situation can fortunately be quickly overcome by rinsing the inside of your tires with a garden hose for a few minutes. Driving your vehicle through a car wash will have the same beneficial effect. b) Hard Linings: This lining is invariably found in brake pads that are used on heavy and large vehicles such as trucks. Unlike the more standard lining, this material does not wear as easily and this makes a squealing noise. c) Low-cost Linings: These linings are not able to cope with the heat build-up caused from continuous breaking in busy high traffic areas and a glaze is formed across their surface, which causes the squealing sound. Other causes include: damaged or weak brake shoe return springs, damaged brake backing plate, and damaged brake shoes
Scraping Sounds: There are two main causes of scraping sounds. The first one could be a foreign body, invariably from the road surface, that has become lodged between the pad and the rotor. The other could be the wear indicator, which might be rubbing against the brake rotor.
Grinding Sounds: Of all the noises associated with brake problems, the most serious is the grinding sound. Most commonly, the friction material has finally been worn away and the metal backing plate is doing the job of stopping your vehicle. Apart from creating a dangerous situation, this situation will cause both your brake rotor as well as the brake calliper to become damaged.
Manufacturers of the majority of GM vehicles include a thin sliver of metal to the brake pad which acts as an indicator when the amount of pad material is no longer acceptable. This clever device can unfortunately cause drivers concern as it produces a whistling-type noise when the brakes have not been depressed. Drivers who are not familiar with this situation may believe that they are experiencing brake problems.
Apart from being an annoyance, any unnatural noise produced by your brakes is an indication that a problem may have occurred, which can make for very dangerous driving conditions. Noises created by your brakes should always be looked into as soon as possible.