The most common and most likely answer to this crossword clue is the 9 letter word RESONATOR
I've seen this crossword clue in Financial Times
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More clues leading to the result RESONATOR
Buddy explains!
The straight part
We know that "One makes sympathetic noises" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one makes sympathetic noises = resonator.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 RESONATOR mean?
RESONATOR noun- Any object or system that resonates
- A hollow cavity whose dimensions are selected so as to resonate at a specific frequency
- A resonant electronic circuit
- A type of musical instrument, especially a guitar, that uses spun metal resonator cones to enhance the sound.