High-pitched sound likely at first in buzzer and piano (5)
I believe the answer is:
bleep
'high-pitched sound' is the definition.
(I've seen this before)
'likely at first in buzzer and piano' is the wordplay.
'at first' suggests taking the first letters.
'in' is an insertion indicator.
'buzzer' becomes 'bee' (I've seen this before).
'and' means one lot of letters go next to another.
'piano' becomes 'p'.
The initial letter of 'likely' is 'l'.
'l' inserted within 'bee' is 'blee'.
'blee'+'p'='BLEEP'
(Other definitions for bleep that I've seen before include "Noise of alarm" , "High-pitched electrical signal" , "High pitched signal" , "High-pitched sound" , "Make short shrill signalling sound" .)