Thanks, guys. It's nice to have a place to talk with people familiar with stoves, and the kind we have in particular.
My husband came home and we opened up the right side door to see what was going on -- by the time he was home, though, the clanking stopped. The example of it sounding like ice in a crusher is pretty much what I heard. My husband said the screws were all tight...but that is something we'll check now & then to be sure of, since now we know they can come loose.
Since everything is working fine now my guess it was a piece of coal getting crushed. Glad to hear that the stoker is robust!! I think I was also a little on edge since we had the faulty circuit board/temp probe at the start that made the stove go all wonky. Now when something is "off" I get more nervous more quickly. But the more I learn, the more comfortable I am. Thanks for all your replies. I really appreciate it.