Let's start with "completely silent", which is a relative concept.
A generator makes noise although next to a calliope it will be
completely unnoticeable.

Of utmost importance is the quality of the power.  Invest is a quality
(industrial) surge suppressor.  All generators have a degree of voltage
fluctuations which needs to be assiduously avoided.  Most importantly,
having produced live events for years, I will tell you that your
biggest concern is loss of power.  This includes generator failure,
people tripping on electric cords and non-enthusiasts pulling plugs.
Therefore you must also purchase an uninterruptible power supply (UPS).

The UPS is basically a battery backup that automatically kicks in to
avoid loss of power if cessation or significant power drop occurs.
Having built the band organ for the Big Apple Circus, it was imperative
that the organ work flawlessly every time it was rolled into the circus
ring.  Even with a sawdust floor and generators as a source of power,
with the proper precautions, you can be relatively assured that your
machine will work flawlessly.

You imply that the music reading system is MIDI.  I especially advise
using the above devices if you are using computer or electronic
controls.

Bob Yorburg
http://www.bobyorburg.com/  http://www.acanthuscarving.com/ 
http://www.youtube.com/watch?v=JIOh3dAo76E&feature=related