I know it's not good to Google, but since I suffer from this, I am the Google queen of internal vibrations. So many people have this and no one knows what causes it. It seems to be a benign condition caused by something unknown but not dangerous. Some of the people who posted said they suffered for years. It isn't pleasant, but if it's nothing that is going to kill me, I have to (unfortunately) live with it. It did get a lot better after I decided to accept it.