Hello,
Following up my request about solutions for detecting where a loud constant humming noise in our house is coming from, can somebody recommend a white noise machine that would suppress the "hum"?
Thank you in advance for your recommendations and help us sleep!

You would get "white noise" if you tuned a radio to an unnused with no signal. That hiss is white noise.

Noise cancelling headsets by Bose (best Buy has them on display) will mask it. Sleeping with them on would be difficult.

I built this for an old girfriend "Surf Synthesizer Feb. 1972 John S. Simonton Popular Electronics. " It worked really really well.

I think there are CD's called "Environments" by David lantz (spelling)

I also found this: White Noise Machines SleepMate 980A Highest Rated Best Sleep Sound (http://www.naturestapestry.com/)

The surf was more soothing than white noise in my opinion.

I don't know if you could go sleuthing for a signal. http://www.reliabilitydirectstore.com/Sound-Level-Meter-p/rdi-ar824.htm?gclid=CJfxiMuz8KACFclM5QodMVtPIA

I would like you to do one thing. Cut the main breaker to the house and see if it goes away. Turn off the water and see if it goes away. Both at the same time.

Are there any wind powered ventilators in the attic.

If these fail, get or get the tool (our utility provides them with a deposit) to turn off the water at the curb stop. You could have an underground leak with no visible puddles.

Thank you for your help. We already tried all your suggestions. Nothing works. I ordered 2 white sound machines to choose the best one. I will also try to tune a radio to an unused with no signal.
I will let you know.