[LibLieSlayer]

I have never heard it when it is raining. I will let you the next time that I hear it. I listened to the You Tube link and the hum that I hear is not so much a buzz... it does sound somewhat like a diesel engine at idle but not quite. That is a close description. I have excellent hearing and I am 58. I also am also fluent in Morse Code at speeds of up to 45 WPM and I have never heard any code characters. I have also heard it just stop... sometimes not returning until the next day... sometimes returning very quickly. I do think that it is using certain resonant structures as transducers because I can only hear it from one room in my house and it is not any external source because I have actively tested and eliminated anything within a 1/2 mile. I live in a very rural area and there is no industry nearby. I do hear a train that has tracks about 2 miles from me but that is distinct and is always heard from anywhere I go... including outside.

[Texan5]

My house is framed in steel-a fad at the time it was built, 11 years ago-the power meter on the pole at the front of the property generates a faint hum that travels along the steel framework and can be heard through the paneling and drywall in most rooms. The first thing I did in my sleuthing was to shut off the power at the pole-the indoor hum quit instantly, but the other one was still heard/felt outside.

[moose07]

Your Description is identical to my experiences of the noise.
It must be emanating from the same ,or similar, source.
It is not the Train service,i live only half a mile from a High-speed line and the noise is still there long after end of service.
Unfortunately i can hear it outside, even in the middle of nowhere.
It has Freepers on its case now, somebody will know. :)