Adverb (fukushi), Adverb taking the 'to' particle
noisily; with loud footsteps
Onomatopoeic or mimetic word
自販機でコーヒーを買おうと１００円入れてボタンを押したら、一気に４本も、どかどかと落ちてきた！When I put 100 yen in and pressed the button to buy a coffee at the vending machine, four cans dropped down all at once! in a crowd; incessantly; all together