rub-a-dub vs drumbeat

rub-a-dub and drumbeat both are nouns.

Word	Noun	Adjective	Verb	Adverb
rub-a-dub	Yes	No	No	No
drumbeat	Yes	No	No	No

As nouns, rub-a-dub and drumbeat are synonyms defined as:

Other synonyms of rub-a-dub include rataplan.

rub-a-dub (noun)	drumbeat (noun)
the sound made by beating a drum	a vehement and vociferous advocacy of a cause
	(military) the beating of a drum as a signal for lowering the flag at sundown
	the sound made by beating a drum