Beater certainly making himself heard! (7)

I believe the answer is:

drummer

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'beater' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

I can't explain the remainder of the clue.

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(Other definitions for drummer that I've seen before include "Musician" , "eg Buddy Rich" , "one of a band" , "dozen Christmas presents" , "Someone who keeps 18 [RHYTHM]" .)

I've seen this clue in the Evening Standard.

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