Happening annually, one unknown listener follows another (4,5,4)
I believe the answer is:
year after year
'happening annually' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'one unknown listener follows another' is the wordplay.
I cannot quite see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
'unknown' could be 'y' (algebra) and 'y' is located in the answer.
'listener' could be 'ear' (body part which hears or listens) and 'ear' is located in the answer.
'another' could be 'r' (I've seen this in other clues) and 'r' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?