Where is that noise coming from? How to tell non-engine noises and vibrations apart
Most noises are diagnosed by their conditions: what the car is doing when the noise appears, and what makes it change. Note speed, braking, steering, road surface and gear before describing it — it is the most useful thing an owner can bring to a workshop.
Map of common causes
| When it happens | Typical sources (not a diagnosis) |
|---|---|
| When braking (pulsation) | Disc thickness variation or hot spots; less often a bent disc or loose components |
| When braking (squeal, grinding) | Pad compound, glazing, worn pads to the backing plate |
| Above about 100 km/h | Wheel balance, tyre defects, irregular tyre wear |
| Over bumps (knock, clunk) | Bushings, anti-roll bar links, top mounts, dampers |
| When steering | Strut top mounts, drive shafts and CV joints, steering rack or tie-rod ends |
| Whistling at speed | Door or window seals (wind noise), mirror or trim gaps; vacuum leaks on the engine side |
| Under acceleration only | Drive shafts, engine or gearbox mounts, propshaft joints |
| Constant hum rising with speed | Wheel bearings, tyre wear, differential |
Starting points for inspection, not conclusions.
The neutral test
If a vibration or hum appears at a certain speed, select neutral at that speed on a safe, straight road (in an automatic, N briefly while coasting). If the noise stays the same, it depends on road speed: wheels, tyres, bearings, drive shafts. If it disappears, it depends on engine load or engine speed: engine mounts, exhaust, transmission or drivetrain under torque.
Bearings and tyres
A wheel bearing hum usually rises with speed and changes when weaving gently left and right, as load shifts from one side to the other. Tyre noise from irregular wear sounds similar but changes with road surface. Swapping wheels front to rear and listening again separates the two.
Bring data, not a diagnosis
A short phone video with sound, the speed, and what you were doing is more useful than a guessed cause. Many noises have more than one possible source; the final answer comes from inspection and road test.
See alsoNoise Troubleshooting →Suspension Repair & Upgrade →