Perhaps the most obvious is to increase precision, which is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the guts distance of the tooth mesh. Sound can be suffering from gear and housing components along with lubricants. In general, be prepared to pay out more for quieter, smoother gears.
Don’t make the error of over-specifying the engine. Remember, the insight pinion on the planetary must be able handle the motor’s result torque. Also, if you’re using a multi-stage gearhead, the result 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 expensive gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, result torque is definitely a linear function of current. So besides safeguarding the gearbox, current limiting also defends the motor and drive by clipping peak torque, which may 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 several 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 generally more expensive than lighter duty types. However, for speedy acceleration and deceleration, a servo-grade gearhead could be the only wise choice. In such applications, the gearhead may be viewed as a mechanical spring. The torsional low backlash planetary gearbox deflection resulting from the spring action adds to backlash, compounding the consequences of free shaft movement.
Servo-grade gearheads incorporate many construction features to reduce torsional stress and deflection. Among the more prevalent are large diameter output shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads tend to be the most costly of planetaries.
The kind of bearings supporting the output shaft depends upon the strain. High radial or axial loads generally 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 capacity. For larger and servo-grade gearheads, heavy duty output shaft bearings are often required.
Like most gears, planetaries make sound. And the quicker they run, the louder they get.

Low-backlash planetary gears are also available in lower ratios. Although some types of gears are generally limited to about 50:1 or more, planetary gearheads prolong from 3:1 (single stage) to 175:1 or even more, depending on the number of stages.