Re: vibration in lower bowel area
Sounds to me like simple intestinal movement. I can literally SEE and FEEL my colon moving about at times, especially when lying on my back. If a person is fairly thin, this is easier to do.
Abdominal rumblings are generally normal and what a doctor hopes to hear with his/her stethoscope. It's usually when there are no "sounds" that there's cause for concern.
If this is bothering you, just go see your family doctor and have him/her listen for a minute. That should reassure you that there is nothing amiss. Our bodies can make some pretty strange sounds, etc., and most of it is perfectly "normal." Above all, don't worry!