Use green, yellow, and red colored cups for group work. When a table gets too loud, change the cup to yellow. If the table continues to be too loud, the cup gets changed to red; this means a loss of group time. Students now have to do their work independently and silently. This is great and won't punish the entire class.
Are you looking for a way to motivate your grade level to have great cafeteria behavior? Here's a great tool to help encourage children to have a quiet and clean cafeteria environment. Teachers decide which class out of the grade level performed the best.