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 materials as well as lubricants. In general, be prepared to spend more for quieter, smoother gears.
Don’t make the error of over-specifying the engine. Remember, the insight pinion on the planetary should be able manage the motor’s result torque. What’s more, if you’re using a multi-stage gearhead, the result stage should be strong enough to soak up the developed torque. Obviously, using a more powerful motor than required will require a bigger and more costly gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, result torque is 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 simultaneously in mesh. Although you can’t really totally eliminate noise from such an assembly, there are many methods 
to reduce it.
As an ancillary benefit, the geometry of planetaries matches the shape of electric motors. Hence the gearhead can be close in diameter to the servomotor, with the output 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 sensible choice. In this kind of applications, the gearhead could be viewed as a mechanical springtime. The torsional deflection resulting from 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 prevalent are large diameter output shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads have a tendency 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 component bearings. Small planetaries can often manage with low-price sleeve bearings or various other economical types with fairly low axial and radial load capacity. For larger and servo-grade gearheads, durable output shaft bearings are usually required.
Like the majority of gears, planetaries make sound. And the quicker they run, the louder they get.
Increase your knowledge of low backlash gearbox.