It is normal that Enner exhibits more noise and hum than traditional synths, it’s inherent to the design and not a sign of a defect. Some days it will feel louder than others, but this will be a subjective experience.
Regarding ground, this is mentioned in the manual:
A normal grounding connection at the electric socket, which is carried through the power cord to your audio equipment to which the ENNER is connected, is sufficient.
This means that, as long as the rest of your studio/apartment/live setup has a proper ground, Enner will be grounded.