Tramps exposed source of music? (4)
I believe the answer is:
oboe
'source of music?' is the definition.
(I've seen this before)
'tramps exposed' is the wordplay.
'tramps' becomes 'hoboes' ('hobo' can be a synonym of 'tramp').
'exposed' says to take the centre (outside letters removed).
The central letters of 'hoboes' are 'OBOE'.
(Other definitions for oboe that I've seen before include "bit of wind" , "blow it!" , "Double-reed wind instrument" , "Instrument used in 1d" , "Cor anglais in its family" .)