What Causes the Squeaking Sound When Braking a Car?

[DelKate]

There are several specific reasons why a car makes a squeaking sound when braking: 1. Use of low-quality or overly hard brake pads. If the brake pads are too hard or of poor quality, they will produce a squeaking noise when rubbing against the brake disc during braking. 2. Presence of sand or other foreign objects between the brake pads and brake disc, which can cause a squeaking sound during braking. 3. Severe wear of the brake disc. Using low-quality brake pads or having foreign objects inside the brake disc can lead to wear on the brake disc. If the brake disc is excessively worn, stepping on the brake will produce a squeaking noise. 4. The brake pads emit a warning sound. The brake disc becomes thinner with use, and if the wear reaches the threshold of the warning line, it will emit a squeaking alarm sound.

[JackDella]

Let me start from the beginning. Just last week, my friend's Sagitar had the exact same issue. The mechanic took it apart and found a small stone stuck between the brake pads. The metal shim rubbing against the brake disc made a screeching noise like chalk on a blackboard. This happens most often in rainy weather—the metal particles in the brake pad coating oxidize when wet, creating a sandpaper-like friction. Another possibility is the wear indicator scraping against the disc, which means your brake pads are almost worn out! When I first installed my aftermarket brake pads, they squealed for the first 200 kilometers. The mechanic said it was normal during the break-in period, and sure enough, they’re silent now. Experienced drivers know that lightly applying the brakes a few times can generate enough heat to remove rust and reduce noise. But if the squealing persists, get it checked ASAP—a stuck caliper could be dangerous.

[DelLaila]

My neighbor, Old Liu, who runs an auto repair shop, taught me a folk remedy: drawing a few chalk lines on the side of the brake pads actually made the noise disappear. That sound is 90% caused by high-frequency vibrations, especially with newly replaced ceramic pads that tend to resist the rotor. Once, I saw them replacing pads on a BMW—they even had to apply a special noise-reducing paste to the rotor, a silver paste that looked like toothpaste smeared on the friction surface. It's more noticeable in winter when frost forms on the rotor surface during cold starts, and metal hard spots directly grind against the iron rotor. If it's a modified rotor with grooves or drilled holes, the squeal can turn into a whooshing sound, which car enthusiasts actually find appealing. But for safety's sake, it's still recommended to test the brake fluid's water content—excessive moisture lowers the boiling point and affects braking performance, with the noise serving as a warning.

[LunaRose]

My colleague's newly acquired Model 3 squeaks when reversing, and Tesla's after-sales service claims it's the normal sound during the transition between regenerative braking and mechanical braking. Many brake pads are designed with metal particles as friction material. When hard points make contact, the temperature instantly soars to 300 degrees—no wonder they scream. I've personally seen technicians use sandpaper to smooth the chamfered edges of brake pads, resolving the noise issue in just three minutes. Those who've modified their brakes should note that performance pads operate starting at 500 degrees, making them prone to uneven wear during daily driving. It's advisable to start lightly applying the brakes 200 meters before a traffic light, allowing the brake temperature to rise gradually. This method is much quieter than cold discs grinding against hard pads.

[DelCody]

A buddy who does car reviews told me that if the brake discs develop wave-like patterns, stepping on the brakes feels like nails scraping a comb. These need to be resurfaced with a specialized lathe, and the labor cost is almost half the price of a new set of brake pads. European cars are particularly prone to squealing because their OEM pads have a higher metal content, while North American cars use ceramic pads for quiet operation but with inferior braking performance. Once, when we disassembled the brakes on an Audi Q5, the anti-noise shim was installed backward, causing the metal to resonate and sound like whistling. After rain, lightly tapping the brakes a couple of times to remove rust is more effective than honking to alert the car ahead. If you hear a clunking sound during hard braking, it’s probably the ABS engaging with its pulsating action—completely normal.

[DavidAnn]

My relative, who has been repairing cars for twenty years, said that brake squealing is mostly due to the caliper pins. If those two stainless steel guide rods lack lubrication, the uneven sliding of the wheel cylinder can cause the brake pads to wear at an angle. Last time, my car had noise from the right front wheel. Upon disassembly, it was found that the rubber boot on the guide rod was cracked and water had seeped in, causing rust that welded metal powder onto the rod. What’s even scarier is that the stabilizer bar bushings were worn out—when braking, the entire chassis would creak and twist, sounding like a brake issue when it was actually a suspension problem. After an automatic car wash, chemical residues left on the wheels can crystallize and grind against the brakes, causing squealing. It’s recommended to brake several times at low speed after washing to clean the surface. Brake noise is much easier to deal with than the clunking sound when turning the steering wheel.