I had exactly this sort of thing happen after a mains water pipe burst
in the flat above, causing a Niagara of water to flow into mine.
No electrical problem was apparent the first time, even though it took
several hours to get the water shut off (I now own my own 'Toby key'
to allow me to do that myself, though that horse had already bolted).
But despite my asking the owner of the upper flat to tell the plumber
she was getting *not* to turn the water back on, the bloody fool did so
and caused another Niagara. (He 'needed' to do this to find the leak,
which I think turned out to be from a frozen combi boiler).
After the second flood, I started to hear small explosions at intervals
of maybe 5 minutes, and tracked those down to a junction box someone
had installed long ago at the back of a high shelf.
(Perhaps not compatible with today's regulations, but well out of the
reach of someone standing on the floor.)
The box had become saturated and seems to have been electrolysing the
water then periodically igniting the resulting gases.
If you had at one time some water ingress, you might have had the same
sort of problem, which could well disappear after everything dried out.
--
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