Subaru WRX STI Grinding noise when braking Inspection at your home or office.

Common reasons for this to happen:

• Excessive Pad Wear: The single most common reason to hear a grinding noise when braking is excessive pad wear. Once the material has been worn off the backing plate, you’ll be experiencing “metal on metal”. Part of the brake caliper could also be touching the rotor at this point. Both cause extensive damage – the backing plate will eat into the rotor, causing grooves and serious damage. The caliper will do the same thing, but the rotor will also eat into the metal of the caliper, potentially causing the need for replacement.

• Foreign Debris Lodged in Brakes: It’s also possible to have foreign debris lodged in the brake system. The most common example would be a rock or piece of gravel caught in the caliper and riding between the caliper and the rotor. This can cause damage to the rotor as well, and you’ll generally hear the sound even when you’re not pressing the brake pedal.

• Low Quality Brake Pads: If you’ve had your brake pads replaced recently and are now hearing a grinding sound, it could be because low quality pads were used. Semi-metallic pads can sometimes contain hard chunks of metal that will eat into the rotors and cause a grinding sound when applied (always use OEM quality brake pads).

• Wear Indicator Contacting Rotor: If the sound you’re hearing is more of a squealing than a grinding, chances are good that it is the wear indicator on your pads connecting with the rotor. This comes preinstalled on many brake pads and is designed to warn you that the pad material is getting low and you’ll need to replace them soon.