Mere claptrap, but good in sound (5)

I believe the answer is:

hokum

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'mere claptrap' is the definition.
'hokum' can be an answer for 'claptrap' (I've seen this before). I am not sure about the 'mere' bit.

'good in sound' is the wordplay.
'good' becomes 'ok'.
'in' means one lot of letters goes inside another.
'sound' becomes 'hum' (humming is a kind of sounding).
'ok' going into 'hum' is 'HOKUM'.

'but' acts as a link.

Can you help me to learn more?

(Other definitions for hokum that I've seen before include "Meaninglessness" , "Bunk" , "gammon" , "Nonsense (colloq.)" , "Sentimental stuff in play or film, nonsense" .)

I've seen this clue in the Evening Standard.

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