If your vehicle is showing loud grinding or growling noise when braking, here are the most likely causes and the parts you'll need to fix each one.
The friction material on the brake pads has completely worn away, causing the steel backing plate to grind directly against the cast iron brake rotor.
Vehicles that sit for extended periods develop heavy surface rust on the rotors. Braking scrapes the pads against this rough rust layer, causing a grinding noise until it wears off.
A small rock, pebble, or piece of road debris can become trapped between the brake pad and the rotor, or behind the dust shield, causing a loud grinding or screeching noise.
A stuck caliper piston or dry, seized slide pins will force the brake pad to drag against the rotor constantly. This leads to rapid, uneven wear and premature metal-to-metal grinding on just one side.
A common DIY or rushed mechanic error where the brake pad is installed with the metal backing plate facing the rotor instead of the friction material, causing immediate grinding.
While usually a constant hum or growl while driving, a bad wheel bearing can sound significantly worse during braking because the vehicle's weight shifts forward, heavily loading the failing bearing.