The most common cause of this is the silent drag mechanism.
Remove the spindle screw and ‘D’ washer, then remove the spool from the back plate.
On the back plate you will see a bronze or brass drag pawl with a pin protruding.
Underneath the spool you will see a cam with a slot.
When assembling the spool to the back plate ensure that the pin on the drag pawl fits into the slot on the cam. This is best done with the drag in the ‘OFF’ position. Now engage the drag in the ‘ON’ position and wind forward. If assembled correctly the reel should now be silent. It may take a couple of goes to correctly assemble.
Now replace the ‘D’ washer and spindle screw.