means To make a deep, continuous, rolling sound — like distant thunder or an empty stomach — or, informally, to fight or to expose something hidden.

from A Middle English word, 'rumblen,' almost certainly imitative — coined from the sound itself, the way 'grumble,' 'mumble,' and 'tumble' all carry that low rolling growl in the 'umble.' It's likely related to similar Dutch and Low German forms (Dutch 'rommelen'), all of them echoing the same deep noise. The street-fight sense ('a rumble') is 20th-century American slang, the brawl named for the menacing low roar that precedes it.