Mostly rehearse zany Ned Flanders' voice (7)
I believe the answer is:
shearer
'ned flanders' voice' is the definition.
I can't tell whether this defines the answer.
'mostly rehearse zany' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'zany' indicates anagramming the letters.
'rehearse' with its final letter taken away is 'rehears'.
'rehears' is an anagram of 'SHEARER'.
Can you help me to learn more?
(Other definitions for shearer that I've seen before include "One that's fleeced" , "Sheep barber?" , "one who removes coat" , "Dancer" , "Man clipping sheep" .)