I would get an electrician to come first. It is most likely he or she who can pinpoint the problem in your house.
I have found a handyman to come and check it out. We turned off the main switch to the house. The noise is still there. The noise is so faint and my handyman cannot hear it. He told me that he is used to a lot more noises. He cannot hear this one. We went through the attic of the house and found nothing. Got other suggestions? Who do I get that can help to identify the sound with an equipment?
NEVER use a handyman for electrical issues. They will burn your house down.
Where is the transformer that feeds your house in relation to your house?
On the street, one far corner of the house. This problem just started 1 week ago.
Do you hear this noise outside by the service drop to the house on the transformer side?
No, I did not. I tried to listen to it. There is no noise.
But you still hear it with the main turned off you said, is this right? Is the main inside or outside the house?
The main is on the side of the house. Yes, when I turn the main off, I can still hear the humming sound. I have Dish network dish on the roof top, would that send out signals despite the main is off? I am not using that dish at all.
No it will not make any sounds at any time. If you turn off the outside main breaker then the noise can't be electrical in nature. Find another person who hears this sound and have them help you track it down. With 2 people you can find it easier.
3 people is better yet, triangulate the sound and pinpoint it.
Is it possible there is a bee nest in a wall of the house? I have no idea what climate you are in if you might have bees coming to life now.
The challenge is that we have high ceiling in the house. It's hard to hear things if it's from the roof top. Could the humming noise be from the bee? Do you know whom I should call that may have the sound detector/identification equipment?
Before you call in someone who will charge you huge fees ask some other friends who might also hear the sound to help you find the source. Try to identify what the sound might be. An exterminator might be in order when you locate the source. I have heard of hornets or wasps nesting in the wall of a house and causing problems.