Drink noisily, not quietly -- what one might do when drunk (4)
I believe the answer is:
slur
'what one might do when drunk' is the definition.
The definition suggests a singular noun which matches the answer.
'drink noisily not quietly' is the wordplay.
'drink noisily' becomes 'slurp' (I've seen this before).
'not' suggests deleting specific letters.
'quietly' becomes 'p' (musical symbol).
'slurp' with 'p' removed is 'SLUR'.
Can you help me to learn more?
(Other definitions for slur that I've seen before include "Pronounce indistinctly - discredit" , "Musical sign: "Run together"" , "Discredit, say reputation" , "Slight lack of distinction in speech" , "Negative comment" .)