The most common and most likely answer to this crossword clue is the 7 letter word WHINGES
I've seen this crossword clue in The Guardian
W
H
I
N
G
E
S
Buddy explains!

The straight part
We know that "complaints" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case complaints = whinges.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 WHINGES mean?
WHINGES noun- A cry.
- A peevish complaint.
- To complain, especially in an annoying or persistent manner.
- To whine.