The most common and most likely answer to this crossword clue is the 9 letter word HARRUMPHS
I've seen this crossword clue in The Times
H
A
R
R
U
M
P
H
S
Buddy explains!

The straight part
We know that "sounds unhappy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sounds unhappy = harrumphs.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 HARRUMPHS mean?
HARRUMPHS noun- An expression of disdain, disbelief, protest, or dismissal; a huff, grunt, or snort.
- To dislike, protest, or dismiss.