Almost shy describing rubbish drums (7)
I believe the answer is:
timpani
'drums' is the definition.
(type of drums)
'almost shy describing rubbish' is the wordplay.
'almost shy' becomes 'timi' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'describing' is an insertion indicator (describe can mean to form the outline of).
'rubbish' becomes 'pan' (both can mean to criticise heavily).
'timi' enclosing 'pan' is 'TIMPANI'.
Can you help me to learn more?
(Other definitions for timpani that I've seen before include "Set of kettledrums" , "PM, I ain't (anag.)" , "part of kitchen?" , "Features of kitchen" , "Percussion instrument" .)