The worm is retained by a collet which screws into the end of the worm block. This thing puts a pre-load on the worm bearings, and is often overtightened by the factory. It makes things ratchety on rotation of the worm. You can try backing this off a bit. The collet is that threaded ring with the two notches. What you would do is remove the worm block and make the collet adjustment until the worm moves smoothly with no axial play.
If you were to try this, be aware the collet is kida fragile and is easy to deform, so if you don't have a tool that can pan those slots and engage correctly you can damage the collet. Ordinarily ES would allow you to try to make this adjustment yourself, but you need to get them to clear this to you directly, given the opportunity to foul up the collet. BTW I ruined one of mine.
But I have to confess I don't believe anyone has had the click symptom you have from the overtightening. Bob's idea that there is something wrong with the worm itself seems likely.
Wes, Southport NC
EXos2-GT PMC-8, iExos 100
ES ED 127, 10" LX200GPS+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired