Pass to defender? That might bring whistling (8)
I believe the answer is:
feedback
'pass to defender? that might bring whistling' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'pass to defender?' is the wordplay.
'pass' becomes 'feed' (I can't justify this - if you can you should give a lot more credence to this answer).
'to defender?' becomes 'back' (I've seen this before).
'feed'+'back'='FEEDBACK'
Can you help me to learn more?
(Other definitions for feedback that I've seen before include "cause of hi-fi distortion?" , "Informative response" , "Responses to customer survey" , "Suggestions to improve performance" , "some whistling?" .)