I would think it is the anti-reverse pawl. Some reels they do not have a "silent" anti reverse bearing, rather they have a ratchet pawl that clicks against one of the large drive gears, very similar to the locking pawl on your boat wench.
You can disengage the anti reverse and the spool will spin backwards to feed out line and the clicking should disappear when you reel in(or be very faint).
I have 4 Ultra light Okumas and one of them has started clicking when I reel in line. I have had it apart 3 times and I can't figure out why it clicks when the others don't.
Mark 1:17 ...I will make you fishers of men