Bell sounding? I must leave (4)
I believe the answer is:
gong
'bell' is the definition.
(I've seen this before)
'sounding? i must leave' is the wordplay.
'sounding?' becomes 'going' ('go' can be a synonym of 'sound').
'must leave' suggests deleting specific letters.
'going' with 'i' taken away is 'GONG'.
(Other definitions for gong that I've seen before include "Dinner call - medal" , "Round plate that resounds when struck" , "Instrument - award" , "Sound it, for dinner say" , "Wordsworth's Boy; Dostoevsky's hero" .)