What causes gear noise at high speed when the gears look well made?

Identify the order and operating condition

Record speed, torque, temperature and lubricant condition when the sound appears. Compare the dominant frequency with shaft orders and gear-mesh frequency. A tone that follows mesh frequency suggests mesh excitation, while a strong resonance may occur only when an excitation crosses a structural mode.

Do not judge from sound level alone. Capture vibration or acoustic data during a controlled speed sweep and note whether the problem changes with load, direction or temperature. AGMA technical literature describes transmission error forces acting through bearings and exciting the housing, which then radiates sound.

Check the gear pair and its supports together

• Tooth geometry: profile, lead, pitch, runout, surface condition and modifications against the approved drawing.
• Loaded alignment: shaft deflection, bearing clearance or preload, housing stiffness, center distance and contact pattern.
• Lubrication: correct type, viscosity, supply and temperature for the operating speed and load.
• Assembly: concentric mounting, balance and any damage or debris introduced after inspection.

A gear may pass a visual check yet still have micrometre-scale errors or an assembly condition that changes contact under load. Inspect the mating pair and the system, not only one loose gear.

Verify the correction under the same test

Choose the remedy only after the source and path are identified. Microgeometry correction, better finishing or tighter runout may reduce mesh excitation; bearing, shaft or housing changes may reduce transmission or amplification; lubrication changes may address frictional or thermal effects.

Repeat the same speed, load and temperature sweep and compare the order spectrum, vibration and sound. A quieter prototype at one speed is not proof across the duty cycle. See PairGears' pages on microgeometry and noise and finishing options for gear whine.