I just noticed this a few days ago. Initially, it was only happening everyonce and a while in reverse, but just today, my dad and I noticed it happening when slowing down in D4 (I have an Auto). It sounds like a really harsh grinding noise from below the driver/passenger seat, so originally we thought it might be the transmission (afterall, it was only happening in reverse originally) but the transmission isn't located in that area so, now we don't know what it might be. It sounds as if something is dragging below the car, but we jacked it up and there aren't any loose parts or anything. Any ideas? It's a really loud grinding noise, as if you were driving along at 40mph and slammed it in to reverse. Could it be the transmission?