Yesterday when making a cast, my spool locked up and made a loud noise (as if I deactivated the spool release- I didn't). Since then, whenever I'm reeling, I hear and feel something clicking. The click happens at the same time during each turn of the reel handle. 

 

When I remove the spool, the clicking stops. But I don't see anything wrong with the spool itself. Any ideas?

You didn´t happen to have your thumb slightly pushing up the thumbar did you ? because for what you say it sounds like that happened, in Daiwa reels you don´t need to turn the handle to engage the spool, you can engage the spool by pushing up the thumbar and if that happens wile spool is rotating then ----> uh oh, you may damage the pinon gear reason why it clicks every time you turn the handle, you turn the handle and the reel makes a ticking sound.

That problem almost always requires a gear set replacement. Don't replace just one; get the set.

bummer.

Check the spool pin. If it's bent, replace it and see if the clicking goes away.

The guys are right. Sounds like the pinion got damaged. If the spool pin got bent, the softer brass of the pinion is undoubtedly damaged. In a wear situation definitely replace both gears. In this case you're probably safe doing just the pinion if there's no visible damage to either mating teeth.