Resonant sound about metal railing (7)
I believe the answer is:
ranting
'resonant sound' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'about metal railing' is the wordplay.
'about' is an insertion indicator.
'metal' becomes 'tin' (tin is a kind of metal).
'railing' becomes 'rang' (I can't explain this - if you can you should believe this answer much more).
'tin' inserted into 'rang' is 'RANTING'.
Can you help me to learn more?
(Other definitions for ranting that I've seen before include "Making a loud and angry speech" , "Raving, haranguing" , "Shouting wildly" .)