How to play the kazoo (3)
I believe the answer is:
hum
'how to play the kazoo' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hum that I've seen before include "Drone or buzz" , "Pong" , "Sound (of business?)" , "Reek" , "Unpleasant smell" .)