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 is also affected by gear and housing materials along with lubricants. In general, be prepared to pay more for quieter, smoother gears.
Don’t make the mistake of over-specifying the electric motor. Remember, the insight pinion on the planetary should be able deal with the motor’s output torque. Also, if you’re utilizing a multi-stage gearhead, the result stage should be strong enough to absorb the developed torque. Obviously, using a better motor than required will require a larger and more expensive gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque is certainly a linear function of current. Therefore besides safeguarding the gearbox, current limiting also defends the electric 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 at the same time in mesh. Although it’s impossible to totally eliminate noise from this assembly, there are many ways to reduce it.
As an 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 output shaft in-line.
Highly rigid (servo grade) gearheads are generally more costly than lighter duty types. However, for fast acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In this kind of applications, the gearhead may be seen as a mechanical spring. The torsional deflection caused by the spring action increases backlash, compounding the effects of free shaft movement.
Servo-grade gearheads incorporate several construction features to reduce 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 tend to be the costliest 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 could manage with low-price sleeve bearings or other economical types with fairly low axial and radial load ability. For bigger and servo-grade gearheads, heavy duty result shaft bearings are often required.
Like the majority of gears, planetaries make sound. And the faster they run, the louder they get.
Click view independent reviews concerning low backlash gearbox.