I am having the same problem. My experience is almost identical to what you described. It’s driving me nuts.
Did you find a solution?
Hello, I was googling this problem and came upon this thread. I have the same problem in my house. Started last fall, didn't notice it much over the winter but in the past weeks I've noticed it again. And like you guys I don't hear it anywhere but inside the house. Sometimes i can ignore it and sometimes it makes me crazy. I live alone so no one to ask if they hear it too.
Did you find a solution to the noise?
I know this is an old thread, but I wanted to add to the list in hopes of finding a solution/cause.
Currently, Turning OFF the water coming into the house makes the low rumbling/humming sound--which is under my raised house--go away.
In my situation:
I'll keep diagnosing and update with a solution should I find one!
gfarra's description of the low frequency vibration sounds identical to ours. It started out of the blue 6 months ago. Our 3,000 sq ft home rumbles 24/7. We have exhausted everything we know to find the cause. Power Company, HVAC, Water Company Engineer visit, private electrician, private plumber, gas company ( 2 small leaks discovered and fixed ), securing storm gutters, ruling out wasps or bee hives, unofficial opinion from a biologist at inland fisheries dept, cable company, phone and doorbell sources ruled out, elaborate hearing eval with excellent results, visit to local factory that makes aluminum ( who were very cooperative and even did 3 experiments to see if the sound which is below 20 hz would disappear when they cut off fans and lowered their reverberatory furnace fire, but there was no change ) and we had to replace the water pressure regulater because the incoming water pressure to the house was 100 psi....it is now 60. 4 people can hear/feel this, but most cannot. If it is not resolved by Spring, I am planning to look for a new home.