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 is also affected by gear and housing components and also lubricants. In general, expect to pay more for quieter, smoother gears.
Don’t make the mistake of over-specifying the engine. Remember, the insight pinion on the planetary must be able manage the motor’s result torque. Also, 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 expensive gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servolow backlash gearbox motors, result torque is certainly a linear function of current. Therefore 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 at the same time in mesh. Although you can’t really totally remove noise from this assembly, there are many 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 result shaft in-line.
Highly rigid (servo grade) gearheads are generally more expensive than lighter duty types. However, for quick acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In this kind of applications, the gearhead could be viewed as a mechanical spring. The torsional deflection resulting from the spring action increases backlash, compounding the effects of free shaft movement.
Servo-grade gearheads incorporate a number of construction features to minimize torsional stress and deflection. Among the more common are large diameter output shafts and beefed up support for satellite-equipment shafts. Stiff or “rigid” gearheads have a tendency 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-price sleeve bearings or other economical types with relatively low axial and radial load capability. For larger and servo-grade gearheads, heavy duty result shaft bearings are usually required.
Like most gears, planetaries make sound. And the quicker they operate, the louder they get.

Low-backlash planetary gears are also obtainable in lower ratios. While 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 more, depending on the number of stages.