The most common and most likely answer to this crossword clue is the 7 letter word RANKLES
I've seen this crossword clue in The Times
R
A
N
K
L
E
S
More clues leading to the result RANKLES
Buddy explains!

The straight part
We know that "Grates" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case grates = rankles.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 RANKLES mean?
RANKLES verb- To cause irritation or deep bitterness.
- To fester.