Have been aware of this phenomenon for a while but just got round to trying to figure out the cause. I assume an electrical disturbance but I can't relate the SES incident to anything going on in my house at the same time. Does anyone else see the same kind of thing or have a clue to what might be causing it? Am attaching a couple of graphs showing the most recent examples. The problem does not recur in the rest of the day as far as I am aware.
