Green’s Dictionary of Slang

pum-pum n.¹

[the ‘pum-pum, pum-pum’ of the tunes]

a fiddler.

[1607		Marston What you will IV i: A fidler, a scraper, a miniken tickler, a pum, a pum].
1890–1904		Farmer & Henley Sl. and Its Analogues (old).