goro-goro
The low, continuous rumble of distant thunder, or the sound of something heavy rolling. Also used for a cat purring (猫がごろごろ). Note: ごろごろする (lounging around) is a separate, non-onomatopoeia usage.
💡Hearing thunder in the distance — 'Thunder is goro-goro rumbling, rain is coming.'
遠くでごろごろと雷が鳴っている。
Thunder is rumbling goro-goro in the distance.
The cat is purring ___ contentedly on my lap.
膝の上で猫が喉を○○と鳴らしている。