Sound from pen and old writing material (4)
I believe the answer is:
oink
'sound from pen' is the definition.
'oink' can be an answer for 'sound' (I have seen 'Sound of pig' mean 'oink' so perhaps 'sound' could also mean 'oink'). I am unsure of the 'from pen' bit.
'old writing material' is the wordplay.
'old' becomes 'o' (abbreviation).
'writing material' becomes 'ink' (substance for writing with).
'o'+'ink'='OINK'
'and' is the link.
Can you help me to learn more?
(Other definitions for oink that I've seen before include "Animal sound" , "Sow's sound" , "Piggish noise" , "Pig's noise" , "it might be in a pen one hears" .)