There is a vibrating sensation in my lower abdomen that came on suddenly. no change in appetite, no nausea, no vomiting. i'm not currently on my period and i am not pregnant. what could it be?

Lots possible...: ...Unless you're pregnant (& you are well advised to check, just to be sure). You may be describing intermittent movement of air through the gut, which some interprete as abdominal "vibrations" or "fluttering" sensations. Of course, there are easy lab and imaging tests your doctor can perform to rule out inflammatory conditions or other medical issues of concern that present similarly.