The most common and most likely answer to this crossword clue is the 9 letter word YODELLING
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result YODELLING
Buddy explains!

The straight part
We know that "Swiss singing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swiss singing = yodelling.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 YODELLING mean?
YODELLING verb- To sing (a song) in such a way that the voice fluctuates rapidly between the normal chest voice and falsetto.
- The act of one who yodels.