Mind snapping a picture by chance? Are you talking about the foam piece that sits in a small plastic frame within the air box itself? If so, from what I have found is that it's an airbox muffler, which essentially reduces air intake noise caused by vibrations. People will sometimes remove this to improve intake sound. I am not sure if there is a part number for that part as most people just toss it, but depending on the material you might be able to use a service kit on it.
2003 Porsche 911 Carrera 4S Coupe - Intake System - Page 1