Perhaps the most obvious is to increase precision, which really is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound can be affected by gear and housing components as well as lubricants. In general, be prepared to pay out more for quieter, smoother gears.
Don’t make the error of over-specifying the motor. Remember, the insight pinion on the planetary must be able deal with the motor’s output torque. What’s more, if you’re using a multi-stage gearhead, the output stage should be strong enough to soak up the developed torque. Obviously, using a more powerful motor than necessary will require a bigger and more expensive gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, output torque is certainly a linear function of current. So besides protecting the gearbox, current limiting also shields the engine and drive by clipping peak torque, which may be from 2.5 to 3.5 times continuous torque.

In each planetary stage, five gears are simultaneously in mesh. Although it’s impossible to totally eliminate noise from this assembly, there are several methods to reduce it.

As an ancillary benefit, the geometry of planetaries fits the shape of electric motors. Therefore the gearhead could be close in diameter to the servomotor, with the output shaft in-line.
Highly rigid (servo grade) gearheads are generally more costly than lighter duty types. However, for speedy acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In such applications, the gearhead may be seen as a mechanical spring. The torsional deflection caused by the spring action increases backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate several worm gearconstruction features to minimize torsional stress and deflection. Among the more prevalent are large diameter output shafts and beefed up support for satellite-equipment shafts. Stiff or “rigid” gearheads tend to be the costliest of planetaries.
The kind of bearings supporting the output shaft depends on the strain. High radial or axial loads usually necessitate rolling component bearings. Small planetaries could get by with low-cost sleeve bearings or additional economical types with relatively low axial and radial load capacity. For larger and servo-grade gearheads, heavy duty output shaft bearings are often required.
Like the majority of gears, planetaries make sound. And the quicker they run, the louder they get.

Low-backlash planetary gears are also low backlash gearbox available in lower ratios. While some types of gears are usually limited to about 50:1 or more, planetary gearheads prolong from 3:1 (one stage) to 175:1 or even more, depending on the amount of stages.