What would cause high frequency power on a bix block?

While attempting to locate a phone line I found some pairs on our bix box that appear to have high frequency high voltage power. The toner tool has a plastic tip to isolate the tool and user from what is being probed. Eventually you find the line that has the tone/signal and it is amplified so you can hear it (along with all the other noise on the line).

However, the energy on these twisted pairs is high enough voltage, and high enough frequency that it actually sustained an arc through the plastic probe itself between the two wires. It looked like what you would get form a neon transformer, however on several sets of twisted pairs on our bix block. The frequency was high enough that the toner didn't produce any audible sounds beyond the initial pop when the plasma starts/stops.

What would cause this? Is there some kind of a device that injects power onto CAT3, but at very high frequency and high voltage? Could this simply be a high power transmitter dumping RF energy into our phone lines?

I'm going to bring my fluke multimeter back to the site tomorrow and try to get some voltages, though I suspect it's going to be over 1000V. It looks dangerous to me because if you were to touch that you would certainly get an RF burn and possibly much worse. These wires are basically unlabelled, they simply have a faded black line on the bix box.