I probably set the gain too high when I was recording. The hum is selfnoise for my recording unit, which is (unfortunately) a video camera. I think it's caused by the motor that drives the tape- with my new tapeless system I think I've reduced this noise quite a bit (for new recordings.) Thanks for the input.
Were they green? If so, they're probably tropical parrots. There's a huge flock that comes by my area every year now, by the hundreds, and they are LOUD... and yes, very annoying. :) The whole flock actually parked right outside my bedroom in the trees this fall and I beat myself up that I didn't have any batteries in my microphone!
The "clicking" happens when a new arc is sparked at the base of the ladder during the dispersion of the previous arc. This is part of how the device works (see the flickr photos for a better idea.) We did find a way to keep an arc "alive" by blowing it down towards the base, but this produces a different noise. You can hear this effect in this sample: http://freesound.iua.upf.edu/samplesViewSingle.php?id=19482
The effect you want can probably only be achieved through postproduction, or recording a different device...