I have a few circuits for EL:
One scavenged from a toy EL rope/string thing.
PC Mod kits with either rope/string EL or Tape kits (cheaper than buying an inverter generally) Like these:
http://tinyurl.com/3wfwbs
I’ve just received the red tape, but it is closer to bright pink! Hmmm 
I can confirm that the EL power supply is almost completely silent with two different normal backlights, with a variable voltage of, say, between 4-12v, a good range of brightness can be had.
It is encapsulated, or potted in a plastic shell about 45mm x 26mm with a self adhesive foam pad in place.
Not super cheap as in near free, but it does have 2 EL connectors, so you could power 2 backlights (MB seq) or use the mod tape as well for some flashy light strips on or inside your project.
I shall buy more of these in the future for EL BL, I’ve tried a few other ones that were noisy.
I also made a circuit with a very small VA transformer, about 240v->12v, reversed and wired up to a 555 timer circuit with adjustable PWM triggering a power transistor to drive it.
The one I made, even though I stuck to the recommended freq. etc. is loud.
I toned down the noise to bearable levels by reducing voltage, but this also reduces brightness..
This noise is not transferred into the synth sound at all.
It’s just a bit annoying, but not as loud as the noise the Yamaha A3000 makes, which is louder than the PC tower..
I’m not whining now (aiiiee)
