Hope this helps someone.

Kept hearing/feeling a click when honing on the yellow side of a Belgian. Honed several blades successfully. Could not feel anything on the stone.

Tonight it just bugged me to the point that I examined it even more carefully. Thought I felt something with pressure on my finger, above the surface of the hone. Under a bright light I noticed a small shiny (think glass) pinpoint where the click was occurring. Dug it out with a pin. No more click.

Posting this only because when I searched under "coticule inclusion" I found posts saying that inclusions in coticules were soft, and that they were usually darker than the surrounding material. Not this one. Definitely harder, and diamond-like.

Maybe a piece of pure quartz?