What Causes Abnormal Noises When a Car Starts at Low Speed?

[Juliet]

Abnormal noises when a car starts at low speed are likely related to the engine. The causes of these noises are as follows: 1. Relationship between abnormal noises and engine speed: Most common engine noises depend on the engine's speed state. (1) Noises only occur at idle or low speeds. Possible causes include: excessive clearance between the piston and cylinder wall; overly tight piston pin or connecting rod bearing assembly; excessive clearance between the tappet and its guide hole; wear on the camshaft profile; sometimes, a loose starter clutch causing pulley noise (more noticeable during speed changes). (2) Noise becomes chaotic at a certain speed, with brief sounds during rapid deceleration. Possible causes include: cracked camshaft timing gear or loose fixing nut; broken crankshaft; loose piston pin bushing; excessive axial clearance of the camshaft or loose bushing. (3) Noises appear during rapid acceleration and persist at high speeds. Possible causes include: loose connecting rod bearing, melted or mismatched bearing shell; loose crankshaft bearing or melted bearing shell; broken piston pin; broken crankshaft. 2. Relationship between abnormal noises and load: Many engine noises are closely related to load. Diagnosis can be done by gradually removing load from each cylinder, typically using single or double cylinder cut-off to identify the relationship between noise and load. (1) Noise disappears or reduces when a cylinder is cut off. Possible causes include: piston slap; loose connecting rod bearing; piston ring leakage; broken piston pin. (2) Noise worsens or appears when a cylinder is cut off. Possible causes include: loose piston pin bushing; excessive piston skirt taper; piston pin displacement; severely loose connecting rod bearing cap bolts or melted connecting rod bearing alloy; severely loose flywheel bolts. (3) Noise reduces or disappears when two adjacent cylinders are cut off. Possible causes include: loose crankshaft bearing.

[PatrickMarie]

I've been repairing cars for over a decade. Common causes of abnormal noises during low-speed startup include: either brake pad issues - they may squeak due to rust after rain; or aging suspension components like cracked stabilizer bar bushings that make popping sounds like squeezing a plastic bottle when going over bumps; if the CV joint is worn out, it'll produce clicking noises when accelerating during turns; also don't overlook cracked engine mounts which cause dull thuds during startup. I recommend checking the brake system first, then lifting the car to inspect undercarriage components, paying special attention to cracked bushings. These parts aren't expensive to fix, but neglecting them can lead to uneven tire wear and alignment issues - don't wait until ball joints detach before addressing the problem.

[DelGia]

Last year, my car made a thumping noise when starting, and I thought it needed a major repair. Turns out, it was just the toolbox in the trunk not being secured properly. Sometimes, these strange noises can really scare you unnecessarily—first, check the items in your car: a loose spare tire mount can rattle, rolling water bottles in the trunk can thump, and a plastic bag stuck under the chassis can rustle. If all these are ruled out, it might be a bad wheel hub bearing—the noise gets louder with speed—or a stone stuck in the brake pads, causing a screech when braking. Once at the repair shop, I watched the mechanic use an endoscope to inspect and found that the exhaust pipe heat shield was deformed and rubbing against the frame; bending it back fixed the issue.

[KalebAnn]

Starting abnormal noises should be judged based on sound characteristics: A metallic squeaking sound usually indicates brake pad wear and requires immediate replacement; A deep thumping noise may come from cracked engine mount rubber; Clicking sounds are mostly caused by CV joint failure. Long-term neglect of transmission fluid changes can lead to torque converter idling noise, while aged belts produce dry screeching sounds. Inspection should proceed from simple to complex: First check if tire pressure is balanced to rule out wheel hub deformation; Then try coasting in neutral—if the noise persists, it's likely a chassis issue; If the noise disappears after hard acceleration during startup, it's probably a loose exhaust hanger.

[OSophie]

Don't ignore abnormal noises from the chassis! Last time, a friend's car made a clunking sound when turning left at low speed, which disappeared at 20 km/h. It turned out to be excessive play in the outer CV joint of the driveshaft – continuing to drive could have led to a breakdown. There are many similar safety hazards: a broken stabilizer link can cause loss of control when cornering; a loose brake caliper bracket may lock the wheels. My advice is to slow down and pull over if you hear unusual noises, then check the temperature of all four wheel hubs by touch. If one is noticeably hotter, it indicates the brake pads aren't retracting properly. Schedule a professional inspection promptly – don't try to fix it by randomly hammering the chassis to save money. Some components require a torque wrench for proper reassembly.

[Judy]

After the first maintenance of the new car, there was a buzzing noise when starting. The 4S store claimed it was a normal phenomenon during the break-in period. However, after driving for two months, it was discovered that six screws on the underbody guard were loose. Therefore, it's crucial to pay close attention during routine maintenance: always tighten the guard plate screws when changing the oil; driving slowly over speed bumps can extend the lifespan of suspension bushings; wash the car after rain to rinse the brake discs and prevent rust. If there's abnormal brake noise, first check the brake pad indicator on the dashboard; for manual transmission cars, inspect the clutch release bearing. Remember three key inspection intervals: check the chassis screws every 5,000 kilometers, inspect the suspension bushings every 20,000 kilometers, and replace the brake discs every 40,000 kilometers.