Inside the factory, the machines rumbled non-stop.
Tips
memory
轰 (hōng) is itself onomatopoeic — three 车 ('cars/wheels') stacked to evoke a loud rumble — plus 鸣 (míng, 'to cry out / sound'). So 轰鸣 = 'rumble-cry', the deep continuous sound of engines, thunder, or heavy machinery.
usage
Used for low, continuous, powerful sounds — engines, jets, thunder, explosions. For sharp single noises use 轰隆 or 巨响 instead.
