It's a subtle fast vibration that repeats continually. There's no pain, but it's almost nauseating, I think because i can't escape it. It's been happening for two days now, and when I press my hand near it, it doesn't stop, but my hand can't feel the vibrating. I do have lots of back issues, but no sciatica problems in my legs; just a lot of pain, sometimes numbing, lots of aching. This vibration is new and I'm a little freaked out about it.