10 Causes of Gearbox Noise and Vibration (and How to Fix Them)

A gearbox tells you what is wrong with it long before it fails — through noise and vibration. The skill is knowing which sound means what. Below are the ten causes we see most often in field investigations, ordered roughly from most to least common, with the check to run and the fix to apply.

1. Shaft misalignment

Symptom: whining or growling that changes with load, often with vibration at twice the running speed.
Check: laser or dial-indicator alignment of the gearbox output to the driven shaft. Look for a worn or cracked coupling element.
Fix: realign to the coupling maker's tolerance and replace the coupling insert. This is the single most common cause of early gearbox failure on coupled drives.

2. Coupling wear or wrong coupling type

Symptom: a rhythmic knock at each revolution, worse at low speed.
Check: inspect the elastomer, pins, or gear teeth inside the coupling.
Fix: fit the correct coupling for the torque and misalignment present. A rigid coupling on a misaligned drive destroys bearings.

3. Loose mounting or soft foot

Symptom: broadband vibration, often worse at one corner of the baseplate.
Check: loosen each bolt in turn and watch the vibration; a change indicates soft foot.
Fix: shim the baseplate, re-torque to spec in a cross pattern.

4. Bearing wear or incorrect preload

Symptom: high-frequency hiss turning into a rumble; in later stages, a distinctive growl at a bearing-specific frequency.
Check: vibration spectrum analysis for bearing defect frequencies; feel for hot bearing housings.
Fix: replace bearings and reset preload or end float to spec.

5. Tooth wear, pitting or a chipped tooth

Symptom: a once-per-revolution knock that is louder under load, sometimes with a visible "notch" you can feel when rocking the shaft.
Check: drain the oil and inspect for metallic particles; borescope through the inspection cover.
Fix: replace the gear set. Continuing to run a chipped tooth destroys the mating gear within hours.

6. Gearbox running at a resonant speed

Symptom: vibration peaks sharply within a narrow speed band and disappears outside it.
Check: run the drive slowly through its speed range and note the rpm at which vibration peaks.
Fix: change the operating speed, or add stiffening or damping to the mounting structure. If a variable speed drive is fitted, lock out the resonant band.

7. Wrong or degraded oil

Symptom: increased noise when hot, overheating, sometimes a change in tone after an oil change.
Check: oil level, viscosity, colour and smell. See our gearbox oil guide.
Fix: drain, flush if contaminated, refill with the correct grade and quantity.

8. Overload or wrong application

Symptom: progressive noise increase with load plus rising temperature.
Check: measure motor current against nameplate; confirm the load matches the original design.
Fix: correct the application, or replace with a correctly rated unit. Note that an undersized unit rarely fails suddenly — it simply wears out early.

9. Foreign objects or debris in the housing

Symptom: sudden onset of irregular grinding or clicking, often after a repair.
Check: drain the oil through a filter and inspect.
Fix: clean the housing completely, replace the oil and the breather. Also inspect the breather for damage — a failed breather admits dust.

10. Structural vibration from the machine itself

Symptom: vibration present even when the gearbox is uncoupled and run alone.
Check: run the gearbox disconnected from the driven machine.
Fix: if the gearbox is quiet alone, the problem is in the machine, the foundation, or the frame. Strengthen the structure or isolate the drive.

A quick diagnostic sequence

1. Run the gearbox uncoupled. Noise gone? The problem is downstream.
2. Check the oil. Colour, level, metal content. Five minutes, eliminates two causes.
3. Check alignment and mounting. Eliminates two more.
4. Measure vibration at the bearings. Identifies bearing and gear defect frequencies.
5. Vary the speed. Identifies resonance.
6. Only then open the unit.

Following that order avoids the most expensive mistake in gearbox troubleshooting: removing a sound gearbox from a machine that was vibrating for a different reason.

WGT supports its installed units with replacement gear sets, bearings, seals and technical advice. Send a description of the noise, a photograph of the nameplate and any vibration readings through the contact page, or see after-sales service.

Frequently asked questions

Is some gearbox noise normal?
Yes. Every gearbox makes some noise, and the level depends on type, speed and load. What matters is a change from the unit's own baseline.

Can I keep running a noisy gearbox?
Only if you can monitor it and you understand the cause. A once-per-revolution knock usually means a damaged tooth and will worsen quickly.

What is the most common single cause?
Misalignment. It is also the cheapest to fix and the most frequently skipped.