100v PA speakers, charged?

That comes from output transormer in the amp itself. Possible.
Just think about it, in normal amp, you have audio signal as relatively low volts high current, in order to power the low impedance of a speaker.
In 100 volt line its other way around.
Especially if you are plugging and unplugging live.
 
I don't recall ever seeing a transformer that could hold a charge. The inductance of a transformer could cause a spark as you disconnect it from a live circuit. But certainly not on a string of speakers. And they store no charges.

The only way to shock yourself from the 100v system is to grab it live when a large signal is present, and that has zero to do with the speakers and small transformers.