Noise after installation is one of the most common reasons customers call back. A gearbox that whines, rattles or grinds after mounting usually points to an installation, lubrication or condition issue rather than a manufacturing defect — but separating those causes on the shop floor takes a disciplined sequence. This guide is a field troubleshooting checklist: it walks through the most common post-installation noise symptoms, what each one usually means, and what you can adjust on site versus what requires returning the gear set to the supplier.
The first symptom to sort out is whether the noise changes with torque. A torque-dependent whine that rises and falls with load, but stays roughly constant in pitch at a given speed, usually points to the mesh itself rather than a bearing or resonance problem. When the whine appears only under load and fades at idle, look first at backlash and contact pattern: if the gears were set too tight during installation, the flanks are running on top of the lubricant film and the mesh is fighting itself. Loosening the mounting, re-shimming the centre distance and re-checking the contact patch on a stain pattern often resolves it without touching the gear teeth. If the whine is present even at no load and tracks speed rather than torque, the cause shifts toward pitch error, runout or a pre-existing surface defect that installation simply revealed.
Misalignment is the second category, and it shows up as a noise that changes when you load one direction versus another. Angular misalignment — shafts not parallel — produces a one-sided contact pattern and a rhythmic knock that pulses once per revolution of the pinion. Parallel offset misalignment tends to produce a broader, harsher whine across the tooth width. On installed gearboxes, the root cause is rarely the gears themselves; it is usually the driven machine's shaft not sitting true, the coupling floating off centre, or the base plate flexing under load. The fix is to re-indicate the input and output shafts, correct the foot shimming, and tighten the mounting bolts in a diagonal sequence so the housing does not twist. Once alignment is restored, the noise usually drops within the first hour of running.
Lubrication starvation sounds different again. It is a high-pitched scratch or grind that gets worse the longer the gearbox runs, because without a proper oil film the flanks begin to touch directly. Check the oil level first, then the oil return and the sight glass — many post-installation complaints come from a gearbox that was mounted in a different orientation than the one it was tested in, so the oil no longer reaches the mesh. If the viscosity is wrong for the speed and temperature, the film collapses under load and the noise returns even with the correct level. Switching to the recommended grade and cycling the unit for thirty minutes usually quietens it; if the grinding persists, the flanks may already have picked up damage that the supplier should inspect.
Wear patterns tell you what the noise has been doing over time. Pulling the inspection cover and looking at the contact patch on the driven gear is the single most informative step in this whole checklist. A uniform, matte contact band across the middle of the tooth means the gears are behaving as designed. Contact riding high on the tip or low on the root points to centre-distance error. Contact squeezed to one edge means angular misalignment. Pitting — small, shiny craters clustered on the pitch line — is surface fatigue and usually appears after months of running, not on day one. If pitting shows up immediately after installation, the load rating was mismatched to the application, and that is a supplier conversation, not a field adjustment.
On site, work the sequence in order. Start by listening: use a long screwdriver or stethoscope held against the housing to localise the noise to the input bearing, the mesh, or the output side. A bearing noise has a finer, higher pitch than the mesh and tends to grow with the bearing's own temperature; a mesh noise tracks the tooth-meshing frequency, which is easy to calculate from the pinion speed and tooth count. If the noise follows a specific component, isolate that component first — loosen the coupling and run the motor alone, then re-engage — so you are not chasing a sound that is actually coming from the driven machine. Then check installation alignment: run an indicator on the coupling faces and the mounting feet, because most callback noise traces back to a mounting error rather than a tooth error. Angular error is the most common and the easiest to introduce when the base plate settles after first bolt-down. Next, check lubrication: level, grade, temperature, and whether the oil is actually reaching the mesh given the mounting orientation. Sight-glass bubbles or a noisy suction line on the pump side tell you air is being drawn in, which on its own generates a lot of noise that has nothing to do with the gears. Only after those three clean checks should you look at the tooth contact pattern itself, because once you pull the cover you have committed to a re-assembly and a run-in period.
Knowing when to stop and call the supplier is as important as knowing what to adjust. Field-adjustable causes are installation alignment, shimming, oil level and oil grade — things you can correct with hand tools and a dial indicator, and things the supplier would rather you try first anyway, because shipping a gear set back and forth costs everyone time and money. Supplier-required causes are pitting that appears in the first weeks, a contact pattern that will not centre no matter how you shim, broken or spalled teeth, and noise that persists after alignment and lubrication are confirmed correct. Unusual symptoms also belong to the supplier's desk: a sudden bang after a year of quiet running, a noise that worsens through a shutdown and restart, or a pattern that looks completely wrong compared to the stain-mark example on the drawing. In those cases, document the symptom, the run hours, the load and the oil grade, photograph the contact pattern, and send it to the supplier before disassembling further. The factory can usually tell from a photograph whether it is a design mismatch, a heat-treatment issue or shipping damage, and whether the gear set needs to come back.
Prevention is always cheaper than troubleshooting, and the best time to eliminate post-installation noise is at the design stage — choosing the right accuracy grade, modifying profiles, controlling backlash and matching materials before the gears are cut. Our companion guide on gear noise and vibration reduction covers those design-side choices in depth, so we will not repeat them here; this checklist exists to handle what shows up after installation. If your gearbox is still noisy after working through these steps, send us the symptom description, a housing photo and the contact-pattern picture. Our ISO 9001 engineering team will help you read the evidence and decide whether the fix is on the floor or on our workbench.