Crowd noise that can hearten Harrow (4)

I believe the answer is:

roar

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'crowd noise' is the definition.
(I've seen this in another clue)

I don't understand the remainder of the clue.

(Other definitions for roar that I've seen before include "engine noise" , "Lion's sound" , "cheer" , "Shout loudly" , "Jaguar, for example, emits this" .)

I've seen this clue in the Evening Standard.

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