Listen to the first sound of the drum pulse (9)
I believe the answer is:
heartbeat
'drum pulse' is the definition.
'heartbeat' can be an answer for 'pulse' (synonyms). I am not certain of the 'drum' bit.
'listen to the first sound' is the wordplay.
'listen to' becomes 'hear' (to hear something is to listen to it).
'first' indicates taking the first letters.
'sound' becomes 'beat' (beat is a kind of sound).
The first letter of 'the' is 't'.
'hear'+'t'+'beat'='HEARTBEAT'
'of the' is the link.
Can you help me to learn more?
(Other definitions for heartbeat that I've seen before include "Circulation noise" , "Essential pulsation" , "Animating force" , "Pulse of cardiac origin" .)