The most common and most likely answer to this crossword clue is the 8 plus 2 plus 3 plus 4 letter word ELEPHANT IN THE ROOM
I've seen this crossword clue in Financial Times
E
L
E
P
H
A
N
T
I
N
T
H
E
R
O
O
M
Buddy explains!
The straight part
We know that "Trumpeter that no-one talks about" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trumpeter that no-one talks about = elephant in the room.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.