My wife and I live in West Rogers Park, Chicago. We've been experiencing this awful hum for some time now. Heard with power main off. No attic fan. Checked gas line, took down roof antenna, gutters are tight, windows good, roof vents tight, etc. Thought it might be an oxidizer from the Federal Mogul plant 1/4 mile away, and it may be, but it doesn't cause a hum in every home, but it does in ours. Chimney cap tight, heard even when heat is off, we don't have a sump pump, believe me we've covered all the bases.
Heard the most around 11 pm until sunrise. Peaks around 4-5am.
Like a truck idling outside, go outside and ...nothing. I don't know if it is possibly water related, I've turned off both toilets, still heard it.
I'm offering a $500 reward/prize to anyone who can detect what is causing it and provide a solution. Seriously.
Last thing... seems to be loudest when temps are roughly 45-65 degrees outside. Ten weeks in spring and fall when I go nuts. Hum is too low for a fan or white noise or ear plugs to block.. not LOUD loud, just low and constant drone, it vibrates your ear. ANYBODY HELP PLEASE?