The most common and most likely answer to this crossword clue is the 11 letter word COMPLAINING
I've seen this crossword clue in The Times
C
O
M
P
L
A
I
N
I
N
G
Buddy explains!

The straight part
We know that "Finding fault" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case finding fault = complaining.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COMPLAINING mean?
COMPLAINING verb- To express feelings of pain, dissatisfaction, or resentment.
- To make a formal accusation or bring a formal charge.
- To creak or squeak, as a timber or wheel.
- The act by which someone complaints; a complaint.