I have lived in my house for about one year. I have never had any noise problems. Within the last two weeks there is a low grade, steady fog horn like sound that is becoming more pronounced. I have turned off the electrical & water mains and it still continues. The water heater is fine as is the plumbing. I have been in the attic and cannot isolate any area where the noise may be coming from. There is a security system that is in the home but it has not been activated since I purchased the home. I did see what appeared to be some antennae like rods in the attic toward the back of the house that I am assuming is for the security system. Granted, I have been tested for hearing while in the military my hearing is more acute than average but this sound just started two weeks ago and I have been here for nearly a year. The weather has changed from the very hot dog days of summer here in Arizona... to nights that are in the 40s now. I am wondering if that could be creating some structural tension that is causing this humming sound.

I see others have posted some years ago about a similar problem. I was wondering if they found the source of their problems and/or a remedy for the problem.

Thanks for your help.

As a rule humming's caused by vibration. Did the plumber check the toilets? Read on.
Sometimes The problem is caused by the ballcock trying to fill while water is seeping out of the tank. The sound it makes is the washer vibrating against the seat of the ballcock. First check there linkage between the flapper and the flush lever. It should have 1/4" of play when your tank is filled. Next feel the flat side of your flapper. Does it have wavey edges? Do your hands come away black? Replace it if it does. And last check the seat itself. Any nicks or rough spots? If so click on back. There are replacement seats that glue right over the old one and are easy to replace. One of the above should take care of your noise. This happened in a new house some years ago. Only at night and in the early morning. They thought the house was haunted and were about to move out. I caught it in the powder room toilet. It would vibrate and the pipes in the wall would pick it up and carry it all over the house.
Just a suggestion. Good luck, Tom

Humming sound can be caused by variety of devices, like...

1. Computer
2. Any kind of speakers
3. RO system
4. TV
5. Flowing water ( sprinklers, drip system, etc... )
6. Hot water circulation pump
7. Busy Freeway close by
8. High voltage electrical wires
9. Neighbor's generator in his RV
10. Pool equipment
11. Radiant floor heating
12. Door bell
13. Any kind of transformer including the one used for Thermostat
14. Street lamp
15. Ceiling fan
16. Electric clock
17. Any electronic device put on Stand By
18. Refrigerator
19. Slowly dripping faucet
20. Leaking Sprinkler Anti-Siphon valve

Just to think of few...