Why Do Brake Discs Make Abnormal Noises?

[HeidiAnn]

The main reasons for abnormal noises from brake discs are as follows: 1. New car causing abnormal noises: Many new cars experience brake noises, which is quite normal because new brake pads and discs need to break in. Sometimes, they may emit slight friction sounds, which usually disappear on their own after driving for a while—no need to worry. 2. Foreign objects between the disc and pad: The most common cause of brake noise is the presence of foreign objects between the brake pad and disc, such as sand or small stones, which can produce a hissing sound when braking, often quite harsh. Usually, the sand or stones will be gone after some time, or you can try slamming the brakes a few times. 3. Rainy day causing abnormal noises: Rainy weather can also lead to brake noises. If the car has been parked for several days, the brake disc and pad may stick together due to rust, possibly making a loud bang when starting again. This is also normal—no need to worry. Pressing the brakes a few times will remove the rust from the disc. Another scenario is a low-speed whining sound when braking, possibly due to water in the brake disc or dampness in the brake pad and disc. The noise will stop once the water dries. 4. Not replacing brake discs in time: Brake discs have a limited lifespan. After prolonged friction, grooves may form on the disc, causing abnormal noises when the brake pad rubs against the groove edges. If the grooves are not too deep, smoothing the edges can solve the noise issue. However, if the grooves are already deep, it's advisable to replace the discs promptly.

[OCole]

I just encountered this situation a couple of days ago, and the mechanic mentioned several common causes. If it's a new car or the brake pads have just been replaced, there's a special coating on the brake disc surface that can produce a sharp friction noise initially, which usually disappears after driving about a hundred kilometers. Rust after rain or car washing is also common, and a few light presses on the brakes can remove the rust. The most troublesome issue is when the edges of the brake disc develop raised ridges, which require removal and machining to fix. Once, I noticed my car always made a squeaking noise at low speeds, and upon inspection, a small stone was stuck between the brake pad's metal plate and the brake disc. Of course, low-quality brake pads with too much metal shavings can also cause persistent noise—my neighbor bought cheap brake pads online that ended up grooving the disc. Finally, a reminder: if you hear a 'clanging' metal knocking sound, it might be a loose caliper, which must be addressed immediately.

[MacEvangeline]

Last time I helped a friend deal with brake noise. The inspection sequence is crucial: first check if the wear indicator is touching the rotor - that small metal tab makes a high-pitched warning sound when contacting the disc surface. Then remove the wheel to inspect the brake pad edges, as oil contamination can create hard spots causing noise. Once, using a borescope, I found my friend's car had a deformed dust shield rubbing against the rotor - gently bending it straight solved the issue. Poor piston retraction causes uneven wear; I've encountered seized guide pins lacking lubrication that produced squeaking sounds. Another hidden cause is oxidation between the brake disc center hole and hub contact surface, requiring sanding treatment. Incorrect aftermarket wheel sizes might also scrape against caliper brackets, needing specialized spacers for proper clearance adjustment.

[MacStephen]

As a female driver who has been driving a manual transmission for eight years, I know all too well the embarrassment of brake squealing. Especially during rush hour traffic jams, that long 'screech—' sound can be heard by the entire line of cars. Once, during a check-up at the 4S shop, the technician said it was because the brake pad anti-squeal grease had dried up, and applying some copper-based lubricant would stop the noise. The 'click' sound commonly heard in winter is actually due to the thermal expansion and contraction of the brake pad backing plate. I remember one time after driving on mountain roads, the brake discs turned a bluish color, and the crackling sounds during cooling were like frying beans. New drivers should take note: if you hear a metallic grinding sound, don't panic—it might just be road anti-slip gravel caught in the brakes.

[SanAlana]

The brake disc noise in our rally team is even more exaggerated. After hard braking at high temperatures, the disc surface crystallizes and produces a screeching sound, necessitating replacement with drilled discs for better heat dissipation. Once during a brake modification, we discovered a shaking noise, which turned out to be due to a disc thickness variation exceeding 0.05mm. Drift enthusiasts have it worse—uneven wear turns their brake discs into polygons, causing a rhythmic humming sound during turns. Street modifications require caution, as racing brake pads operate at high temperatures and are constantly noisy during daily commutes. Last time, using a thermal imaging camera, we found localized temperatures reaching 800°C due to misaligned calipers, and the sizzling sound was downright painful to hear.

[SanNathan]

Some interesting data from my friend's auto repair shop: 70% of brake squealing noises come from metal debris. The copper wires/steel wool fibers in brake pads create scraping sounds when contacting rotors, especially with the low-metallic formulas used in German cars. A BMW owner complained about a 'buzzing' vibration—disassembly revealed two broken cooling fins on the brake rotor. Japanese cars commonly experience aged guide pin bushings, producing a 'clunk' sound during braking like joint dislocation. The most peculiar case involves supercars with aftermarket carbon-ceramic discs—their rustling noise at low temperatures resembles fingernails on a chalkboard, which is normal. A reminder for northern drivers: that 'pop' sound at -20°C is the brake disc contracting and squeezing the caliper.