Pulsing stomach

What you are experiencing are muscles twitches or fasciculations.
They could be symptom of a relatively rare disorder of the nervous system, known as muscle fasciculation syndrome.
It is characterized by the uncontrolled fasciculations (twitching) of muscle groups in various parts of the body, even affecting the abdominal muscles.
Sometimes, it can be associated with muscle cramps and in that case it is known as cramp fasciculation syndrome.
This condition is benign (doesn't get worse over time), and can be present from time to time or constantly.
The cause is most of the time unknown or may follow use of certain drugs, or it may appear after exercise, viral illness like stomach flu or after excessive stress and anxiety.
The basic problem in all of these causes is believed to be a low levels of magnesium.
You may try some magnesium supplements, but, it will be a good idea to see a neurologist, too (sometimes, these fasciculations are symptoms of multiple sclerosis, myastenia gravis, or other more serious neurological diseases).

Best wishes!
Marija