Noise is unexpected result (6)
I believe the answer is:
rustle
'noise' is the definition.
(I know that rustle is a type of noise)
'unexpected result' is the wordplay.
'unexpected' is an anagram indicator.
'result' with letters rearranged gives 'RUSTLE'.
'is' acts as a link.
(Other definitions for rustle that I've seen before include "The sound of leaves in the wind" , "Result (anag.)" , "Wind-in-leaves noise" , "Steal ((eg, cattle)" , "Make sound as of paper crumpling - or steal cattle" .)