This is a common complaint with many Asian supplied machines.
You need to take a service ground to a main ground point and set up what is known as a Star GND.
It is also wise from the 'noise' point of view to ground all metalic parts of the machine to this point, and wire all GND terminal points to this also.
All motor frames and VFD/motor combo's also require a earth GND conductor.
Search here for earthing and grounding, there have been many previous posts.
Al.