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 suffering from gear and housing components along with lubricants. In general, be prepared to spend 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 handle the motor’s output torque. Also, if you’re using a multi-stage gearhead, the result stage should be strong enough to soak up the developed torque. Certainly, using a better motor than necessary will require a larger and more costly gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, result torque is a linear function of current. So besides protecting the gearbox, current limiting also defends the electric motor 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 low backlash planetary gearbox ancillary benefit, the geometry of planetaries matches the shape of electric motors. Thus the gearhead can be close in diameter to the servomotor, with the result shaft in-line.
Highly rigid (servo grade) gearheads are usually more costly than lighter duty types. However, for fast 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 deflection caused by the spring action increases backlash, compounding the consequences of free shaft movement.
Servo-grade gearheads incorporate several construction features to minimize torsional stress and deflection. Among the more common 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 type of bearings supporting the output shaft depends on the strain. High radial or axial loads generally necessitate rolling element bearings. Small planetaries can often manage with low-cost sleeve bearings or additional economical types with relatively low axial and radial load ability. For larger and servo-grade gearheads, durable output shaft bearings are usually required.
Like most gears, planetaries make noise. And the faster they operate, 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 and up, planetary gearheads expand from 3:1 (solitary stage) to 175:1 or even more, depending on the amount of stages.