Repetitive themes, perhaps, played on piano in American shop (6)
I believe the answer is:
tropes
'repetitive themes' is the definition.
'tropes' can be an answer for 'themes' (trope can mean a theme or idea). I'm not sure about the 'repetitive' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for tropes that I've seen before include "Figures of speech, figurative usages of words" , "Poster for figures of speech" , "Figures of speech - pest or what?" .)