Inner
市 — a bustling marketplace, source of noise and crowds. Combined with the gate above, the picture is 'a market scene visible through the gate' = a din, a hubbub. The traditional
鬧 had
鬥 (fight) outside, picturing a brawl in the market. Hence
闹 covers cheerful bustle (
热闹) and angry quarrels (
闹翻).