Shout rebounds within valley (4)
I believe the answer is:
yell
'shout' is the definition.
(yelling is a kind of shouting)
I cannot understand how the rest of the clue works.
(Other definitions for yell that I've seen before include "Shetland isle" , "Howl" , "Shout - Shetland island" , "Loud sharp cry" , "Loud utterance" .)