Gang in class which might be playing noisily? (8)
I believe the answer is:
cassette
'which might be playing noisily?' is the definition.
(cassette tape)
'gang in class' is the wordplay.
'gang' becomes 'set' (set of people).
'in' is an insertion indicator.
'class' becomes 'caste' (type of social class).
'set' going into 'caste' is 'CASSETTE'.
(Other definitions for cassette that I've seen before include "recording device" , "Test case (anag.)" , "Small sealed case of magnetic tape" , "Test case about tape container" , "Vintage recording" .)