This might be tinkling piano kept in the box file (9)
I believe the answer is:
telephone
'this might be tinkling piano kept in' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'box file' is the wordplay.
'box' becomes 'tele' (I've seen this in other clues).
'file' becomes 'phone' (I can't explain this - if you can you should give a lot more credence to this answer).
'tele'+'phone'='TELEPHONE'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for telephone that I've seen before include "Electronic voice transmitter" , "Transmitter of spoken words" , "Book with an alphabetical list of subscribers and numbers" , "Worldwide system of communication" , "Electronic sound equipment" .)