Why is there a sound of grinding brake discs when the car starts?

[NatalieMarie]

There is a sound of grinding brake discs when the car starts because the friction material in the brake pads is too hard. Below is relevant information about brake pads: 1. Concept: A brake disc, simply put, is a round disc that rotates as the car moves. The brake caliper clamps the brake disc to generate braking force. When the brakes are applied, it clamps the brake disc to slow down or stop the car. Brake discs provide effective braking and are easier to maintain than drum brakes. 2. Function: Brake discs and pads certainly serve a braking function, with the braking force coming from the brake caliper. Generally, standard brake calipers have a fixed inner section where the brake piston pump is located, while the outer section is a clamp-like structure. The inner brake pad is fixed to the piston pump, and the outer brake pad is fixed to the outer part of the caliper. The piston is pushed by the pressure from the brake fluid line, moving the inner brake pad, while the reaction force pulls the caliper, causing the outer brake pad to move inward. Both pads press against the brake disc, generating braking force through friction between the disc and the inner and outer pads. In this process, the piston is pushed by brake fluid, also known as hydraulic oil, which is used to assist the engine. For the handbrake, a cable is used through a lever mechanism to forcibly pull the brake pads, pressing them against the brake disc to generate braking force.

[LeVanessa]

I hear a grinding noise from the brakes as soon as I start the car. This is quite common, mainly caused by rust on the brake discs after the vehicle has been parked for a long time. Especially in humid weather, the surface of the brake discs is prone to rust spots, and the metal friction when braking after starting produces noise, which usually disappears within a few minutes. However, if it happens every time you start the car, the brake discs might be uneven or there could be foreign objects stuck in them. I've encountered a similar issue before—it was dust accumulated in the gaps of the brake pads, and a simple cleaning fixed it. When parking, try to choose a dry spot. After rain, lightly press the brakes a few times before driving to warm them up, which can help prevent rust. If the noise persists or gets louder, don’t delay—take your car to a professional shop to check the braking system to avoid accelerated wear and safety risks. My car now undergoes regular maintenance, and such issues rarely occur.