Swiss singing almost weird in loud performance? (9)
I believe the answer is:
yodelling
'swiss singing' is the definition.
'almost weird in loud performance?' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'weird' becomes 'odd' (I've seen this before).
'in' means one lot of letters goes inside another.
'loud performance?' becomes 'yelling'.
'odd' with its final letter removed is 'od'.
'od' placed inside 'yelling' is 'YODELLING'.
(Other definitions for yodelling that I've seen before include "singing style" , "making offpeak call" .)