My son, 36, feels minor sensitive feeling under right rib if he taps on it.. he had a cbc/urinalysis, both were fine, been going on for 13 months now.. no other symptoms at all, doesnt smoke or drink, no effect from food, what could it be?

What you described does not seem to a health issue. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV vaccine. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines