Perhaps the most obvious is to increase precision, which is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound is also suffering from gear and housing components in addition to lubricants. In general, expect to pay out more for quieter, smoother gears.
Don’t make the error of over-specifying the electric motor. Remember, the input pinion on the planetary must be able deal with the motor’s output torque. Also, if you’re utilizing a multi-stage gearhead, the output stage must be strong enough to soak up the developed torque. Obviously, using a more powerful motor than required will require a larger and more costly gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, output torque is certainly a linear function of current. Therefore besides protecting the gearbox, current limiting also shields the electric motor and drive by 
clipping peak torque, which can be 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 remove noise from this assembly, there are many ways to reduce it.
As an ancillary benefit, the geometry of planetaries fits the form of electric motors. Hence the gearhead can be close in diameter to the servomotor, with the result shaft in-line.
Highly rigid (servo grade) gearheads are usually more expensive than lighter duty types. However, for rapid acceleration and deceleration, a servo-grade gearhead could be the only wise choice. In such applications, the gearhead may be viewed as a mechanical springtime. The torsional deflection caused by the spring action increases backlash, compounding the consequences of free shaft motion.
Servo-grade gearheads incorporate a number of construction features to reduce 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 have a tendency to be the costliest of planetaries.
The kind of bearings supporting the output shaft depends upon the strain. High radial or axial loads usually necessitate low backlash gearbox rolling component bearings. Small planetaries can often get by with low-price sleeve bearings or additional economical types with relatively low axial and radial load capacity. For bigger and servo-grade gearheads, durable 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 obtainable in lower ratios. While some types of gears are usually limited by about 50:1 and up, planetary gearheads expand from 3:1 (single stage) to 175:1 or even more, depending on the amount of stages.