I had a bad grinding noise in my Prius this morning. I looked under the car and didn't see anything. I called roadside assistance and soon had a tow truck on site and got the car towed to the dealership. They found that a branch got caught on the exhaust and was rubbing on a wheel. When I got the car I found that somehow it had gained two squares on the fuel gauge!
Glad to hear it wasn't anyting more serious than a stick stuck underneath there. Every now and then I would get a tumbleweekd stuck under my car. Not the Prius though. Haven't had that experience yet and will do what I can to avoid it.