Turn on mike. Sound's beginning to echo and reflect (4)
I believe the answer is:
muse
'reflect' is the definition.
('muse' can be a synonym of 'reflect')
'turn on mike sound's beginning to echo' is the wordplay.
'turn' becomes 'u' (a 'U-turn' is a kind of turn).
'on' is an insertion indicator.
'mike sound' becomes 'ms' (this could be a standard abbreviation which I don't know about).
'beginning to' indicates taking the first letters.
The initial letter of 'echo' is 'e'.
'u' put inside 'ms' is 'mus'.
'mus'+'e'='MUSE'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for muse that I've seen before include "Be absorbed in thought" , "Source of inspiration; rock group" , "Goddess; rock group" , "Inspiration for poet etc - ponder" , "Think - goddess of the liberal arts" .)