Sound happy to turn up resistance, twice (4)
I believe the answer is:
purr
'sound happy' is the definition.
(I've seen this before)
'turn up resistance twice' is the wordplay.
'turn' says the letters should be written backwards.
'resistance' becomes 'r' (electronics abbreviation).
'twice' says to double the letters.
'up' reversed gives 'pu'.
'r' duplicated is 'rr'.
'pu'+'rr'='PURR'
'to' acts as a link.
(Other definitions for purr that I've seen before include "Cat's coo" , "Show pleasure" , "content? I might" , "Sound of a contented feline" , "Satisfaction from queen" .)