Church's part obvious in sound plot (10)

I believe the answer is:

clerestory

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'part obvious in sound plot' is the definition.
'clerestory' can be an answer for 'part' (I have seen 'Part of church' mean 'clerestory' so perhaps 'part' could also mean 'clerestory'). I am not sure about the 'obvious in sound plot' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for clerestory that I've seen before include "Upper story of large church, admitting light" , "Part of church" , "topmost church windows" , "Upper row of windows" .)

I've seen this clue in The Guardian.

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