Stepper motors natural behavior that it moves in steps instead of a continues motion does generate vibrations that transforms to sound giving it it´s classical sound. In some applications a more quiet operation is needed and we have been working to find a solution for this. On the Ultimaker printers where the extruder is mounted on the back plate the vibrations transfers to the rear panel that will actually amplify the sound generated making it louder. In order to solve this we have developed a new mount that uses a special type of foam material that isolates the motor from the mount itself greatly reducing the sound generated. Our now mount is included in all Ultimaker upgrade kits and is also available as a separate purchase. This mount is 3D printed in a professional industrial SLS printer in very strong nylon and then painted in black color.
The mount is available here