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 can be affected by gear and housing components as well as lubricants. In general, be prepared to pay more for quieter, smoother gears.
Don’t make the mistake of over-specifying the motor. Remember, the input pinion on the planetary should be able handle the motor’s result torque. What’s more, if you’re using a multi-stage gearhead, the output stage should be strong enough to absorb 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, result torque is usually a linear function of current. Therefore besides protecting the gearbox, current limiting also protects 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 at the same time in mesh. Although you can’t really totally eliminate noise from such an assembly, there are many ways to reduce it.
As an ancillary benefit, the geometry of planetaries matches the shape of electric motors. Hence 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 rapid acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In such applications, the gearhead may be seen as a mechanical springtime. The torsional deflection caused by the spring action adds to backlash, compounding the consequences of free shaft motion.
Servo-grade gearheads incorporate several construction features to minimize torsional stress and deflection. Among the more prevalent are large diameter result shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads have a tendency 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 element bearings. Small planetaries can often manage with low-cost sleeve bearings or other economical types with fairly low axial and radial load capability. For larger and servo-grade gearheads, 
heavy duty output shaft bearings are often required.
Like the majority of gears, planetaries make noise. And the faster they operate, the louder they get.
Low-backlash planetary gears are also obtainable in lower ratios. While some types of gears are generally limited by about 50:1 and up, planetary gearheads extend from 3:1 (single stage) to 175:1 or even more, low backlash gearbox depending on the number of stages.