Remember class 242?
It has another amazing acoustic feature I didn't mention the last time.
It's designed to work with 25 kV AC, now, what's the one thing this voltage, alternating, does? Arcs. It's not easy to disconnect two pieces of a circuit without an electric arc.
So there is actually a chamber inside that does that. Arc happens there, but it is contained.
It's also f...ng loud. So of course the driver had to do it when I was walking next to the locomotive.
@pony I can sometimes hear the arc at the main station here when they lower the pantographs for mainline trains to/from London (UK also uses 25 000V AC for all overhead railway power) but it never seemed that loud to me. We still use these old things. I am not sure how the noise/flash is suppressed (or even if it is at all).