Peice fell while I was driving!!!!!!

I was driving and suddenly a peice fell off of my 1998 Altima GXE. I got out and picked up the part (on the highway!!!!) but I'm not sure what it is. It appears to be some sort of protective cover for an exhaust part? It seems that the two bracets that were holding it up have rusted and broken. The peice has an overall rectangular shape to it with many small holes on the bottom and it cups or bends around the edges (like an open tray?). It doesn't have a part number, just says "Nissa" and "X 3". it's too narrow to cover the muffler.Anyone know remotely what I'm talking about?

Go to a Nissan dealship and go to the Parts dept. and ask them how much for this part (hand it to them). Tell them the model and year of your car. They will identify it and price it for you. YOU can decide if you want to order a new one or get one at a junk yard.