When first I built my Farmbot a few years ago, the Z axis, particularly when going upwards, sounded like a hybrid of a lawnmower and a two-stroke motorcycle.
Various attempts to quieten it down so that it was only audible from a couple of blocks away, were met with limited success. A fault however, with the original Farmduino led to its replacement with a later version, and the reduction in noise was astounding - no more angry neighbors etc.
With the new Farmduino, the back door had to be opened to hear the Farmbot at all.
This brings me to the July Software update. The farmbot is now so quiet, that you do not know if it is moving, even with the door open, unless you watch it. I am now thinking about a flashing light to indicate activity.