What goes "hmm...errr" all through the night?

No not my better half snoring.
It sounded like a nail gun compressor, or the power-washer when you've switched it off but haven't unplugged it. Hmm...errr. It started about 2 AM and continued at five minute intervals. I got up and checked the dryer: Off. And the pond pump: Off. And the oil burner: Definitely off. I thought it might possibly be the neighbour's airco unit. It was odd and irritating and disturbed my sleep all night long. This morning I discovered that every time the Hmm...errr occurred the lights flickered. Obviously it was our problem and I was going to have to track it down.



The one thing I didn't think of was the pool pump because I noticed it was off on Monday. It was completely still out there, and as no-one is brave enough to get into the unheated pool now, I thought I'd just leave it off until the guys come and close it up for the winter.
Well, guess what? Having exhausted all other possibilities, we checked the pump and the electrical unit was still on although the pump wasn't functioning. We turned the timer off and voila, silence. So I'm pretty sure that means we'll need a new part or pump or whole freakin' electrical unit next Spring.
Ho, hum, errr......