Frank quietly interrupts one, somehow (4)
I believe the answer is:
open
'frank' is the definition.
(synonyms)
'quietly interrupts one somehow' is the wordplay.
'quietly' becomes 'p' (musical symbol).
'interrupts' is an insertion indicator.
'somehow' is an anagram indicator.
'one' with letters rearranged gives 'oen'.
'p' going within 'oen' is 'OPEN'.
(Other definitions for open that I've seen before include "Public" , "Accessible - candid" , "Frank and unlocked" , "such a verdict?" , "Ready for business; spread out; manifest" .)