What Causes the Metal Friction Sound When Getting on the Rear Wheel of a BMW 5 Series?
3 Answers
BMW 5 Series rear wheels producing a metal friction sound can be due to brake break-in, normal ABS system activation, metal hard spots on brake pads, severe brake disc wear, and other reasons. The details are as follows: Brake Break-in: New cars or recently replaced brake discs and pads have a break-in period, during which some noise is unavoidable. Therefore, they need to be worn in, which can cause noise, including vibration friction and sharp squealing sounds. This usually disappears after driving a few hundred kilometers. Normal ABS System Activation: During emergency braking, the brake pedal may produce a continuous thumping sound, sometimes accompanied by a pulsating sensation, indicating that the ABS system is activated. This is a normal sound. Metal Hard Spots on Brake Pads: Brake pads may contain small metal particles, which can produce sharp, piercing sounds when lightly braking. This issue can be resolved by forcefully applying the brakes several times, removing and regrinding the brake pads, or replacing them with higher-quality ones. Severe Brake Disc Wear: Brake disc wear can create deep grooves around the disc's edge, causing noise when the brake pads rub against these grooves. If the grooves are not too deep, grinding the edges of the brake pads to avoid contact with the grooves can solve the problem. If the grooves are very deep, it is recommended to replace the brake disc. Generally, it is advised to replace the brake disc after changing the brake pads twice.
I've been driving for over a decade and have encountered the metallic friction sound from BMW 5 Series rear wheels several times. The most common cause is nearly worn-out brake pads, especially when you hear a squeaking noise—it's likely the brake disc rubbing against the wear indicator. It could also be a faulty wheel bearing, which produces a creaking sound when rotating, or aging and loose ball joints or bushings in the suspension system, causing metallic clanging. I remember once on a long drive, this sound suddenly appeared, and after checking, it turned out to be a small stone stuck in the brake disc gap—removing it fixed the issue. But don’t take it lightly; the rear wheel structure of a BMW is intricate. It’s best to jack up the car and briefly locate the sound source. If you can’t handle it yourself, head straight to a repair shop for diagnosis to prevent the problem from worsening. Safety comes first—never gamble your driving safety on noise.
If you hear metal grinding noises, you can try doing a simple check yourself. First, park on level ground, engage the parking brake, squat down and use a flashlight to inspect the inner side of the rear wheels—check how much thickness is left on the brake pads. If they're extremely thin or metal is showing, it means they're worn out. Also, check if there are any small stones stuck in the tires; these are often overlooked, but removing them might eliminate the noise. Spin the wheel and listen to where the sound is coming from; a rattling noise might point to the braking system, while a humming sound is likely a wheel bearing issue. This job isn't difficult, and you can use a jack and a wrench as tools, but safety is crucial—never get under the car. If you find any issues, fixing them early can save you big money later. DIY enthusiasts should tackle things this way—a BMW 5 Series isn't too complex for DIY work.
