Sounds like someone at the door calling back ‘Bye-bye sailor’ (3-1-3)
I believe the answer is:
rat-a-tat
'sounds like someone at the door calling' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'back bye-bye sailor' is the wordplay.
'back' is a reversal indicator.
'bye-bye' becomes 'ta ta' (I've seen this in another clue).
'sailor' becomes 'tar' (slang term for a sailor).
'tata'+'tar'='tatatar'
'tatatar' backwards is 'RAT-A-TAT'.
Can you help me to learn more?
(Other definitions for rat-a-tat that I've seen before include "Noise of knocking" , "Rapping sound" , "Knocking sound" .)