Monotonous sound of personnel in corporation (5)
I believe the answer is:
thrum
'monotonous sound' is the definition.
(I've seen this in another clue)
'personnel in corporation' is the wordplay.
'personnel' becomes 'hr' (Human Resources).
'in' means one lot of letters goes inside another.
'corporation' becomes 'tum' (I've seen this before).
'hr' inserted into 'tum' is 'THRUM'.
'of' acts as a link.
(Other definitions for thrum that I've seen before include "Make monotonous sound as on guitar" , "Continuous rhythmic humming sound" , "something fibrous" , "Make a rhythmic humming sound" , "Rhythmic buzzing sound - fringe left after weaving" .)