It sounds like some kind of heater coming on. A small 500w heater.?.
Or maybe an old attic fan that comes on when it gets real hot up there..
I have one, but it used far less than 500w..
If you can monitor when the
Mystery load comes on, you might be able to hear it clicking,
if you poke around while the TV and radio is off..
I was outdoors the other day, checking my electric meter and I was seeing about
360 to 420 watts being used all the time. (6 to 7 LCD pluses per minute).
When suddenly, I started getting very erratic busts of quick LCD changes.
Back inside, I find my wife boiling some water on the stove.
The heating element is switching off and on ever 10 or 12 seconds..
I decided it was too hot outside to take more data..
I'm thinking of getting her one of those little induction heater-hot-plates,
since they have to be a lot greener than that dumb stove top.