Rachael’s rear brake developed a pretty serious problem this afternoon - a loud mechanical clicking/racheting sound.  It came on rather suddenly and spontaneously.  The only remedy I could come up with was to loosen it so much that there’s essentially no stopping power in that brake.   Fortunately the rest of the day’s ride was absolutely flat, so we were fine for the day.

We’re still pretty new to disc brakes and their issues, and I don’t recognize this one.  Worn pads?  Something broken?  What are the possibilities here?

An update

Thanks to everyone who offered suggestions and theories.  As well as appreciating the moral support, it was educational.  I especially appreciated Patrick sending an image of what the pads and spring look like.

I have one other theory to offer though: in biking along a crappy, rough dirt path beside Lake Varano yesterday, something jumped up off the path and lodged in her brake pads, causing a sudden onset of abrasion and chattering.

This fits the primary symptom (sudden onset), as well as the second symptom that developed later: the sudden end of the primary symptom. I discovered this when I rode her bike over to the LBS in Foggia a few minutes ago, after it opened for the afternoon.  Before taking it in to show the mechanic though, I retightened the brake so that the problem would be apparent and I wouldn’t look like a fool.  I was of course quite surprised to find that her brake is now fine; and in fact it now functions  better than mine.

So, my theory is that whatever lodged into her brake yesterday dislodged sometime afterwards - maybe rattling along the cobblestones last night in Lesina or even when we arrived in Foggia awhile ago.  In any case, we’re whole and happy again.  Case closed.