No one seems industrious enough any more to use the Oxford English Dictionary, which goes into the history of the word in detail, with many quotes.

The word first surfaces in print in Cour de Leon and in 1315 in Brut as a "meaningless combination of syllables serving as a refrain, orig. sung by sailors when rowing."
From Cour de Leon: They rowede hard and sungge ther too, with heuelow and rumbeloo." This usage continued, along with others, given below, into the 1700s.

The word also used as a place-name:
1530- Hickscomer, "I have been in Gene and in Cowe, also in the londe of Rumbelowe,..."

Also used to mean a blow or stroke:
1400- Land Troy Book,..., He gave him such a rumbelow, That he went ouer his sadil-bowe."

Also to mean rumbling, or resounding 1582, etc.

Also to mean "a woman of light behaviour:"
1611- J. Davies "Then yee descend, where he sits in a Gondolow With Eggs thrown at him by a wanton Room-be-low."

Also to mean a type of carriage:
1881- Blackmore, "Let the other flys, and rumbelows, come down first."

Enough? I suppose some will continue to invent new meanings rather than accept any authority.

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One more interesting quote, with bearing on the overdone thread "Hal and Tow:
1790- Gentl. Mag. LX.. "I have recollected the first verse of the song used on that day (i. c., Flora, Day at Helston, Cornwall)... "Hel-an-tow, Rumbelow.""