Sound currency including sterling (5)
I believe the answer is:
clash
'sound' is the definition.
(clash is a kind of sound)
'currency including sterling' is the wordplay.
'currency' becomes 'cash' (cash is a kind of currency**).
'including' indicates putting letters inside.
'sterling' becomes 'l'.
'cash' going around 'l' is 'CLASH'.
(Other definitions for clash that I've seen before include "Disagree violently" , "Conflict, discord" , "(Of colours) look inappropriate together" , "Forceful disagreement" , "Loud noise - conflict" .)