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 and also 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 output torque. Also, if you’re utilizing a multi-stage gearhead, the output stage should be strong enough to soak up the developed torque. Certainly, using a better motor than necessary will require a larger and more expensive gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque is low backlash planetary gearbox definitely a linear function of current. So besides protecting the gearbox, current limiting also protects the 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 concurrently in mesh. Although you can’t really totally eliminate noise from such an assembly, there are several ways to reduce it.

As an ancillary benefit, the geometry of planetaries matches the shape of electric motors. Therefore the gearhead can be close in diameter to the servomotor, with the output shaft in-line.
Highly rigid (servo grade) gearheads are usually more costly than lighter duty types. However, for rapid acceleration and deceleration, a servo-grade gearhead may be the only sensible choice. In this kind of applications, the gearhead may be seen as a mechanical springtime. The torsional deflection caused by the spring action adds to backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate many construction features to reduce 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 kind of bearings supporting the output shaft depends on the load. High radial or axial loads generally necessitate rolling element bearings. Small planetaries can often get by with low-cost sleeve bearings or other economical types with relatively low axial and radial load ability. For larger and servo-grade gearheads, durable result shaft bearings are usually required.
Like most gears, planetaries make noise. And the faster they run, the louder they get.

Low-backlash planetary gears are also available in lower ratios. Although some types of gears are usually limited by about 50:1 and up, planetary gearheads prolong from 3:1 (solitary stage) to 175:1 or more, depending on the amount of stages.