What Causes the Noise When the Car Just Starts Moving?
3 Answers
This is likely the sound generated by the friction between the brake pads and brake discs, which is a normal occurrence. Detailed explanations are as follows: 1. The braking system of a car consists of the master cylinder, vacuum booster, brake caliper, brake pads, and brake discs. When the brake pedal is pressed, the brake pads clamp onto the brake discs, converting kinetic energy into heat to slow down the vehicle. 2. After pressing the brake pedal, the vacuum booster provides assistance, helping the driver to press the pedal more easily. Upon opening the engine hood, a black metal disc can be seen below the windshield on the driver's side—this is the vacuum booster. 3. In front of the vacuum booster is the master cylinder, which has a reservoir for holding brake fluid. The brake caliper, which contains pistons, serves as the brake slave cylinder.
My old car made a squeaking noise when starting last time, and it turned out the suspension had aged. Rubber bushings harden and crack over time, causing rubber friction sounds when the chassis is compressed during startup. Another time, the brake pads didn’t retract properly, producing a metallic scraping sound when lightly braking while starting. If the engine mount rubber is damaged, the engine will shake and create a clunking sound at the moment of startup. Worn steering system ball joints are also a common cause, especially noticeable when turning while starting. It’s recommended to lift the car at a repair shop to inspect the chassis bushings and check the brake caliper retraction. Replace any aged parts as needed—safety comes first.
Starting noise requires identifying the sound location. A 'squeaking' sound from the engine compartment may indicate aging or slipping of the alternator belt - spraying water on it briefly can confirm (if noise disappears, it's belt-related). A 'clicking' sound from the chassis warrants attention to CV joint wear, especially noticeable during steering. For rear-wheel drive vehicles, check the driveshaft universal joint - metallic knocking sounds indicate looseness. Worn exhaust pipe rubber hangers cause dull rattling from pipe movement. Recommended method: Have someone listen outside during cold starts to easily locate faults. Pro tip: Regularly ask technicians to tighten chassis bolts during maintenance, as many noises stem from loose fasteners.
