Two cats in a drum? (3-3)
I believe the answer is:
tom-tom
'a drum?' is the definition.
(I've seen this before)
'two cats' is the wordplay.
'two cats' can mean two substitutions for 'cat'.
'cat' becomes 'tom' (a tom is a male cat).
'cat' becomes 'tom' (a tom is a male cat).
'tom'+'tom'='TOM-TOM'
'in' acts as a link.
(Other definitions for tom-tom that I've seen before include "African drum beaten with hands, sounds repetitive" , "African drum on the double?" , "Type of native American drum" , "Drum - the piper's son (3-3);" , "Hand-beaten drum" .)