It hums a note for us to hear (3)
I believe the answer is:
bee
'it hums a note for us to hear' is the definition.
The definition suggests a singular noun which matches the answer.
'it hums a note' is the wordplay.
I cannot really see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found in the answer.
'note' could be 'e' (musical note) and 'e' is located in the answer.
A single letter 'b' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for bee that I've seen before include "Honey maker" , "Honey producer" , "In one's bonnet, it's an obsessive idea" , "Busy person" , "Hive worker" .)