Grunt name adopted by yokel (4)
I believe the answer is:
oink
'grunt' is the definition.
(I've seen this before)
'name adopted by yokel' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'yokel' becomes 'oik'.
'n' inserted inside 'oik' is 'OINK'.
(Other definitions for oink that I've seen before include "Swine sound" , "Noise made by a pig" , "Porker's cry" , "Sow's sound" , "Sound from a sty" .)