I heard a popping sound, like large rain drop falling on metal, and located a critter that looked somewhat like either a larvae, or a flat worm or such on the window sill, about 1/2 inch long and maybe 1/16 inch wide... one end, about 20% of the critter would lift and make a popping sound I could hear over the TV from about 20 feet away. There was a spider, appears to be a black widow, also fascinated by the critter, hovering around it. Any ideas?

What you describe is the larva of an Anobiid wood boring beetle, often called a Deathwatch Beetle.

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7418.html

You will need to have your home inspected for powderpost beetles and get estimates for treatment. It won't be cheap.

Adult click beetles, (family Elateridae), bend at the thorax to make a clicking sound. Click here for a YouTube video of a click beetle.