Well, see if he will go jogging up the street and back, to where he breaks a sweat, and then see if he winds up with the same burping. IF he does, then he has too much
gas in his digestive tract that needs to be reduced. If he does not have that burping after running all around the neighborhood, then could be in the evening he is eating or drinking something that creates gas, like carbonated drinks or certain foods, which I will mention below, that he should not indulge in at that time.