Click
Either what gamachinist said, or there's a rough spot or tool mark on the
disconnect where the sear spring bears against it. Also could be a toolmark
on the face of the disconnect where it bears against the trigger or a sharp
edge or burr on the trigger stirrup that's snagging the edge of the disconnect
as the trigger moves. The cure is in polishing things up a little...lightly.
To check for the top of the disconnect hitting the notch in the slide, remove the slide and see if it goes away. (Don't let the hammer fall with the slide removed. Ease it down) If the click goes away, scrape the slot a little.
If it doesn't time to tend to the prep work on the discoinnect, the tips of the sear spring, and the trigger stirrup.
If you have a Dremel or other similar moto-tool...take it out in the street and hit it with a hammer 5 or 6 times so you won't be tempted to use it.
Flat, hard surfaces with fine grit (600-800) wet or dry paper with a little
light oil for the final polish. Lightly break sharp corners or edges with a medium India stone. Polish flat surfaces in a figure-eight pattern with light
pressure on the part. When you polish the 48 degree angle on the rear of the disconnect, be very careful not to change the angle, and remove only
enough material to smooth things up. The tips of the sear spring fingers should be polished on an angle, and don't put a lot of pressure on the fingers,
or you may bend them.
Luck!