The noise becomes more noticeable in late afternoon, although this morning when I awoke it was buzzing away. Sounds sort of like a lot of katydids, or electrical crickets, on and on, sometimes louder, but seems to come from behind & above me in every room. I've noticed it ever since we moved into this house, but now I'm alone and it seems worse of course. This is winter in Oregon, no insects around. It sounds electric, high-pitched, buzzing & I've turned off everything I can think of & noise isn't affected.

Look for weak relays for light timers and bad switches. Also, contact your local power company and have them check that the transformer is functioning properly.

Best you can do is shut off the Main breaker for your home to kill all power in the home to see if that helps. Otherwise follow Don's advice and call the power company out to see if the noise is from their equipment.

It is difficult to diagnosis noise problems over the internet.

I have turned off all the circuit breakers but it doesn't make any difference.
I no one else can suggest anything I will try the power company, thanks
Billye