I'll take it in to the shop this weekend to see what they say, but meanwhile, what say you?

Here's the story. This morning, for the first time in a couple of months maybe, I took the Propel out for a one hour ride before work. Everything worked fine; however, almost every time I braked, or stopped pedaling the bike would emit this weird squawking noise - a sort of raspy, grating squeal. As loud as a squealing brake, but not related to pressure on the brakes. It would stop as soon as I started turning the cranks again, but it would kick in again if I didn't keep the crank turning. So it wasn't very predictable, but it only occurred after braking or when coasting/soft pedaling, but I didn't have to be on the brakes for the sound to continue.

Any ideas as to the cause? Any info I could add to help solve the mystery?