Ultegra 16t cog clicking noise

Hive mind - I have an issue that I've noticed over two different bikes (cassettes) now and for which I've not yet found a solution.

I noticed that I am getting a very audible click from the cassette when in the 16t cog (Being in the big ring or small ring makes no difference). At first I thought it was an indexing problem (it may still be!) because it sounds a little like a badly indexed derailleur. However on closer inspection I have found that the noise is happening once a cassette rotation and occurs on the same tooth every time (as you'd expect). What appears to be happening is that each time the chain hits this tooth it is delayed settling on to the cog just enough to make an audible click when it does.

Now, to add some context this has happened with two ultegra 11-28 cassettes (both with ultegra 11spd chains) on different bikes, one built up by myself and one brand new and factory built - all components different. I can find sporadic references to this on the internet and even the suggestion that it is a known issue (which seems odd) but nothing certain or very recent. Cassette is properly secured, freehub un-notched and hanger properly aligned. The wheel (thru axle) is properly secured. In all other respects everything is properly indexed and set (b-screw etc). Fiddling around with chain tension does nothing.

Has anyone come across this? If so does anyone have a solution. Am I missing something really dumb?

Try to move the two screws

Try to move the two screws

This is about the worst advice possible.

Limit screws and a cog part way through the block have absolutely nothing to do with each other. You'd be more likely to fix the problem by adjusting the front brake on a different bike than by messing with limit screws.

Is there anything obviously different about the tooth in question?

Ie does it look twisted or bent?

Could be the tooth is cut away or something to aid shifting and as such is more prone to damage?

Do you have a cassette tool? Ensure the lockring is tighten up sufficiently to eliminate any movement of the sprockets.

Yeah the cassette is solid and the tooth in question looks normal. Have heard it suggested that it might be a manufacturing defect but this seems very odd.

Going to try replacing the chain as a cheap first option.

So, I fixed this. Took a cone spanner and pried apart the teeth that were catching just enough to clear. Smooth and silent again. Wheel will probably fall off next week.