It's still about Bill - the romantic type heard under the balcony (8)
I believe the answer is:
serenade
'romantic type heard under the balcony' is the definition.
I can't judge whether this defines the answer.
'it's still about bill' is the wordplay.
'it's still' becomes 'serene' (I've seen this before).
'about' indicates putting letters inside.
'bill' becomes 'ad' (advertisement stuck on wall).
'serene' enclosing 'ad' is 'SERENADE'.
'the' acts as a link.
Can you help me to learn more?
(Other definitions for serenade that I've seen before include "Open-air song" , "Murder" , "Piece of music for lovers at night" , "Song to a lover" , "composition" .)