Mystery constant, fast, and barely audible vibration in private home
I had the exact same problem for over two years and sometimes I could hear the vibration. It drove me just about crazy. I would feel it when I laid down in my bed, lay on the floor, standing in the kitchen, laying on my couch, etc. the vibration and sometimes noise would come and go and odd thing is that some people said they felt it but most could not.  I tried everything to trace the vibration down. Checked with my neighbors but no one had the problem. Call specialist but they were honest and said that it would cost a small fortune to set up equipment and no gaurentee that they would find any thing. I add the water and electricity company check it out, both negative. I went on line and found people around the world (English speaking) had the same problem but no solutions.
Then one early morning around 3 am laying in bed the solution came to me. I realized it and that morning I booked an appointment with my GP. I told him about feeling these vibrations and sometimes noise and told him I think it is my body that is actually vibrating. He never heard of such a problem. I beg him for sleeping pills so I could get a good nights sleep. He reluctantly gave me a 5 day supply.
For 5 days I took the pills, slept well, and the vibrations stopped.
Every once in awhile the vibrations come back, like tonight which prompted me to write this and post it on line.
But that is because I've been under stress and not sleeping well. I'll take some 5mg Melatonin (find it among vitamins in drug store) along with a glass of warm milk, get a good nights sleep - may take a few nights of good sound sleep, rest my body, and the vibrations will go away.