The most common and most likely answer to this crossword clue is the 6 plus 4 letter word TURNED DOWN
I've seen this crossword clue in Financial Times
T
U
R
N
E
D
D
O
W
N
Buddy explains!
The straight part
We know that "Said no to/decreased volume" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case said no to/decreased volume = turned down.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.