Heard singer produce a note (6)
I believe the answer is:
tenner
'a note' is the definition.
(ten pound note)
'heard singer' is the wordplay.
'heard' indicates a 'sounds like' (homophone) clue.
'singer' becomes 'tenor' (tenor is a kind of singer).
'tenor' is a homophone of 'TENNER'.
'produce' acts as a link.
(Other definitions for tenner that I've seen before include "A spot of money" , "PS10" , "Banknote (informal); sounds like a singer" , "Cash note" , "little money" .)