Perhaps the most obvious is to increase precision, which really is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the guts distance of the tooth mesh. Sound is also suffering from gear and housing materials along with lubricants. In general, be prepared to pay more for quieter, smoother gears.
Don’t make the mistake of over-specifying the engine. Remember, the insight pinion on the planetary should be able deal with the motor’s output torque. Also, if you’re utilizing a multi-stage gearhead, the output stage should be strong enough to soak up the developed torque. Obviously, using a better motor than necessary will require a larger and more costly gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, result torque is certainly a linear function of current. Therefore besides safeguarding the gearbox, current limiting also defends the electric motor and drive by clipping peak torque, which can be anywhere from 2.5 to 3.5 times continuous torque.
In each planetary stage, five gears are concurrently in mesh. Although you can’t really totally get rid of noise from such an assembly, there are many ways to reduce it.
As an ancillary benefit, the geometry of planetaries matches the form of electric motors. Thus the gearhead can be close in diameter to the servomotor, with the result shaft in-line.
Highly rigid (servo grade) gearheads are generally more costly than lighter duty types. However, for quick acceleration and deceleration, a servo-grade gearhead could be the only wise choice. In this kind of applications, the gearhead could be viewed as 
a mechanical springtime. The torsional deflection caused by the spring action adds to backlash, compounding the consequences of free shaft movement.
Servo-grade gearheads incorporate several construction features to minimize torsional stress and deflection. Among the more common are large diameter result shafts and beefed up support for satellite-equipment shafts. Stiff or “rigid” gearheads tend to be the most costly of planetaries.
The type of bearings supporting the output shaft depends upon the load. High radial or axial loads generally necessitate rolling element bearings. Small planetaries could get by with low-cost sleeve bearings or additional economical types with relatively low axial and radial load capacity. For bigger and servo-grade gearheads, durable result shaft bearings are often required.
Like the majority of gears, planetaries make sound. And the quicker they run, the louder they obtain.
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