Initially I thought the problem was software - so I spent hours over the past few months systematically eliminating each piece of software. And nothing changed!
So then I started on the hardware, and got down to a bare minimum system and to a point where I could show (or so I thought) that it was the motherboard that was at fault. But when Gigabyte tested the motherboard, they put one of their CPUs in it and voila! - the problem disappeared....put my CPU back in, and back came the problem!