If you've opened up the inverter you can see that it's not an Adafruit product, and not from any high-end PCB fab. The PCB fabrication technology looks pretty cheap (it still works), though the price is nice and the enclosure is great. I like the AA batteries instead of a 9V that I've seen in another EL wire inverter.
I would definitely be in the market for a PCB upgrade though, since the noise is not trivial. If anyone knows enough about these circuits to make a schematic/board layout that would be interchangeable with the original PCB it'd be worth a few extra bucks for that upgrade. It'd be nice to have an option for a more expensive but "quiet" (high frequency) inverter, along side the cheaper 3kHz option.
Since there is a multi-function button on the circuit, I'm guessing there's a microcontroller in there, which makes things a little more complicated, right? I've seen an alternate design that uses a 3-position slide switch, which might remove the need for a microcontroller "brain", but I don't have access to it to take some pics. I'll post some pics if I can get them of the 9V/slide switch inverter PCB.
EDIT: It looks like SparkFun also has a 3.3V EL inverter (different design, no battery enclosure) that according to a few commentators is 4kHz. So about the same frequency, same input voltage. I hoped for a schematic, but no luck: I'm guessing it's also a COTS part. I'm guessing it probably sounds the same.
EDIT2: This is another discussion of EL Inverter theory: http://el-wire.tribe.net/thread/293c400 ... ba9132e3bc
. I see from the thread that westfw knows a bit about EL wire -- changing the frequency might be undesirable if it makes the EL wire dimmer.