In this video Lars explains Trinamics spreadCycle™ & stealthChop™ technologies and shows stepper motors running without noise.
Stepper-Motors are robust and cheap, but not silent. Even if the times that stepper-motors have been driven in voltage control full- or halfstep mode, they still have the reputation of being noisy. With modern control modes and careful layout it is now possible to design completely silent stepper-motor drives. Read full article (German language) at all-electronics.net