When i stand up and i rub my tummy with a bit of force i can feel little grooves like the size of a grain of rice inside (not on top of the skin) all over my abdomen. i am a bit over weight. is this something i should be worried about?

Usually very fit people may have a rippling sensation when rubbing their abdominal muscles. You state you're overweight, though. I wonder if you're palpating tiny fatty deposits under the skin. In any event I don't think you have any serious pathology of your abdominal wall. If you still have concerns, have your physician examine and advise you.