I like to post these stories in the non-so-remote chance that somebody else has a similar problem and they're looking for a solution. Today my son called me and said he had hit a pothole and now there was this horrible sound that appeared to be coming from the rear of the car, maybe the right wheel.
He had pulled over to the side of the road and we swapped cars so that I could drive the car the mile or so back home. At very low speeds, there was no noticeable sound. But once I hit, say, 20mph the racket was deeply unsettling: a kind of metal-on-metal sound that resembled a grinding noise. Considering he said he had hit a pothole, I thought it may have been a wheel bearing or something in the rear disc brakes. This made some sense because the sound got louder and more frequent as the speed increased. But here's the counter-fact: there was no shaking of the wheel, no vibration, and no pulling of the car to one side or the other. In fact, the car seemed to run fine except for the awful noise.
I came home and jacked the right rear tire then gave it a shake to check the bearing; it was OK. I pulled the wheel off and nothing really appeared out of the ordinary. I was stumped so I called my neighbor, who has much more experience than me.
Almost right away, he found the culprit: there is a thin metal heat shield around the exhaust running down the center of the underside. The pothole must have popped a rivet and it was loose. When air flowed under the car, it rattled back and forth making a racket but otherwise it didn't affect the drive.
Easy - and cheap - fix with a couple of self-tapping screws.