The most common and most likely answer to this crossword clue is the 9 letter word DEBUGGING
I've seen this crossword clue in The Guardian
D
E
B
U
G
G
I
N
G
Buddy explains!

The straight part
We know that "Finding fault with" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case finding fault with = debugging.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 DEBUGGING mean?
DEBUGGING verb- To search for and eliminate malfunctioning elements or errors in something, especially a computer program or machinery.
- To remove a hidden electronic surveillance device from (somewhere).
- To remove insects from (somewhere), especially lice.
- The process of finding and resolving bugs or defects that prevent correct operation of computer software or a system.