What is the least likely source of noise if brakes squeal each time they are applied?

Choosing glazed brake pads as the least likely source of squealing noise when brakes are applied is understood in the context of how brake components function and the mechanisms that typically produce noise.

When brake pads are glazed, it means that they have become hardened and shiny due to excessive heat, which can contribute to squeaking or squealing noises when applied. However, while this condition does affect braking performance and can produce some noise, it tends to be more associated with a continuous or persistent noise rather than a noise that occurs specifically each time the brake is applied.

On the other hand, worn brake rotors can lead to uneven contact with the brake pads, causing a more consistent squealing sound each time the brakes are applied. Loose calipers can create a situation where the pads do not engage with the rotor consistently, also resulting in noise. Faulty wheel bearings can produce a whining or grinding sound, but they can also create noise when brakes are applied due to improper alignment or movement of the wheel assembly.

In this context, while all factors can lead to various noises, glazed brake pads are the least likely reason for a consistent squeal occurring every time the brakes are applied. This makes it the correct choice in understanding the nuances of brake noise diagnosis.