Mike in high-pitched voice to shake (7)
I believe the answer is:
tremble
'to shake' is the definition.
(trembling is a kind of shaking)
'mike in high-pitched voice' is the wordplay.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'high pitched voice' becomes 'treble' (I've seen this before).
'm' inserted inside 'treble' is 'TREMBLE'.
(Other definitions for tremble that I've seen before include "Look nervous" , "Shudder" , "Quakers do this" , "Shake - quiver" , "Shiver or jerk quickly" .)