The Audi is back, and it appears to be all better. The diagnosis was a broken front left axle, which, no doubt, is yet more fallout from my winter sojourn into a curb. Were it not for that one, stupid, low-speed accident, the car would have never had any problems. I hope the damage from that incident is finally being worked out of the system, because this is the third time I've had to take the car in for repairs related to it. This is why I don't like the idea of buying used cars.
In any case, the dealership chose to treat this as a warranty repair, which was very good news. Saved me something in the neighborhood of $550. I'm not sure if they forgot about the curb mishap, or they didn't, but were helping me out. In either case, it's good to not have to pay for it.