Was sorry for sounding so unpleasant (4)
I believe the answer is:
rued
'was sorry for' is the definition.
(to rue something is to regret it)
'sounding so unpleasant' is the wordplay.
I cannot really understand how this works, but
'sounding' could be 'e' (I've seen this in other clues) and 'e' is located in the answer.
The remaining letters 'rud' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for rued that I've seen before include "Bitterly regretted" , "was remorseful" , "Was contrite about" , "Was sorry" , "'Regretted, repented (4)'" .)