Wear indicators
The front brake pads are equipped with a metal loop that comes into contact with the disc if the rubbing surface has worn almost to a minimum. The wear indicators make a constant, distinct metallic sound that is easy to hear. A similar sound can be described as the sound produced by scratching a blackboard with nails or by crickets in a field. A sign that this is a wear indicator and not some other brake noise is the audible sound when the car is moving WITHOUT using the brakes. (There may be no sound during braking.)
It should be noted that, due to the nature of the design, no disc brake system can work quietly under any circumstances. Each system includes various pads, plates, and suspensions to dampen brake noise, but not all noise is completely eliminated. Some brake noise - high or low frequency - can be controlled and possibly reduced, but cannot be completely suppressed.
Inspection
Front brake pads can be inspected without removing. Having lifted and securely fastened in front of the car, remove the wheel (A). Unlock the steering lock and turn the wheel so that the brake caliper comes out from under the fender.
View the pads - inner and outer - through the window in the center of the caliper. Look at the thickness of the rubbing surface of the pad (the part that actually compresses the disk), which is more important than the thickness of the support shield, which does not change with wear. Replace the brake pads if the thickness is less than 2.4mm.
Keep in mind that you are looking at the profile of the pad, not the entire pad. Brake pads may wear to a cone that may not be visible. It is also not possible to check the contact surface for splits or cracks from this position. This quick way of checking is only relatively useful; detailed inspection requires removal.