It's battery - powered with an automatic night shut - off sensor for silent operation during resting hours. (geekwrapped.com)
The ZERO RPM mode on this model gives a basically silent operation at medium and low loads, and superior regulation in terms of voltage. (thatvideogameblog.com)
However, what is not typical is the smooth power delivery and nearly silent operation of the Malibu Hybrid. (bestride.com)