I had the clicking on retracts as well, it was caused by the gears not meshing together tightly enough. can only suggest whats been suggested already and that is loosen the motor and push together and tighten it up again... I feel your pain with the whole grub screw situation thats the biggest reason i moved to @Chase.Wichert titan 2 setup what a pleasure it is now to adjust nozzles up and down....
I've done that a couple of times but I cannot get rid of the backlash between the gears but it is minimised, perhaps @Greg Holloway will provide some feedback.
Thanks for that, good to know I'm not the only one with this problem. I guess more fiddling is the answer! I definitely plan to upgrade to Chase's design at some point, but I wanted to get it all working stock before playing around with it. Plus that gives him a chance to iterate a bit and for it be road-tested
I think I've found a possible cause of my clicking. On one of my Titans the black filament guide isn't held completely tightly against the Bowden adaptor and when the filament retracts it actually moves very slightly and then settles back causing the clicking. On the other Titan which doesn't click the filament guide is really snug and I can't even move it by hand. I may try to print a very thin shim piece to prevent it moving around and see if that helps.
Actually now I've had a think it would make more sense just to swap the Titans over. For me the one that clicks is the direct one, and it's hard to control the length of the PTFE tube pushing up into the filament guide other than by recutting it since the hot end is pushed up as far as it can go into the carriage, and it can vary a bit as the nozzle is adjusted anyway. If I swap it to the Bowden I can just push the feed tube in a bit tighter to stop it clicking. I suspect it's just down to tolerances, since with nothing else fitted on one it's a really tight squeeze to fit the Bowden adapter and the filament guide into the Titan whereas on the one that clicks it just slides in really easily and hence can move around a bit.