Two cats with small drums (3-4)

'drums' is the definition.
(I've seen this before)

'two cats with small' is the wordplay.
'two cats' means two substitutions for 'cat'.
'cat' becomes 'tom' (a tom is a male cat).
'cat' becomes 'tom' (a tom is a male cat).
'with' says to put letters next to each other.
'small' becomes 's' (abbreviation - e.g. clothes size).
'tom'+'tom'+'s'='TOM-TOMS'