During swindle note aberration (8)
I believe the answer is:
straying
'aberration' is the definition.
(thesaurus)
'during swindle note' is the wordplay.
'during' indicates putting letters inside.
'swindle' becomes 'sting' (sting is a kind of swindle).
'note' becomes 'ray' (I've seen this before**).
'sting' going around 'ray' is 'STRAYING'.
(Other definitions for straying that I've seen before include "Errant" , "aberration" , "Getting sidetracked" , "Drifters may be" , "Wandering from a direct course" .)