Hasted,in his History of Kent, vol iii p 390, speaking of Folkestone,says, "there was a singular custom used of long time by the fishermen of this place. They chose eight of the largest and best whitings out of every boat, when they came home from that fishery, and sold them apart from the rest, and out of the money arising from them they made a feast every Christmas Eve, which they called a 'Rumbald'

Different time of year to the Helston festival, and not St Michael, but still in honour of a Fisherman's saint, apparently.

and:-
the Online Etymological Dictionary gives -
Rumba: 1919, from Cuban Spanish rumba, originally "spree, carousal," derived from Spanish rumbo "spree, party," No doubt seafaring men would be familiar with Spanish words. Connections with Europe of our South coast existed before the Roman era.

And regarding the more modern use of the word 'Rumble' I'm sure there could be a parallel with the change in meaning from 'Bransle' to 'Brawl' - A dance with liquid refreshment and then the inevitable consequences! Jigging about, and cavorting, (gavotting?) have moved in the same direction.