Was sorry about making vulgar sound (4)
I believe the answer is:
rued
'was sorry about' is the definition.
(I've seen this before)
'vulgar sound' is the wordplay.
'vulgar' becomes 'rude' (I've seen this before).
'sound' shows a homophone (sound like).
'rude' is a homophone of 'RUED'.
'making' acts as a link.
(Other definitions for rued that I've seen before include "was remorseful" , "Was sorry" , "Was contrite about" , "'Regretted, repented (4)'" , "Bitterly regretted" .)