がたんごとん

が

た

ん

ご

と

ん

Meanings

1

adverb, adverb taking the 'to' particle

clickety-clack; clatter

onomatopoeic or mimetic word

Onomatopoeia for the rhythmic sound of a train or similar mechanical clattering, often used with と.

がたん
がたん is a single sharp clattering sound, while がたんごとん is a repeated, rhythmic clatter.
ごとん
ごとん is a single heavy thud or clunk, while がたんごとん combines lighter and heavier clattering sounds.

Onomatopoeic formation from がたん (a clattering sound) and ごとん (a heavier thud), mimicking the alternating sounds of a train on tracks.