Unscrew the plastic cap Is there supposed to be a metal flap that covers the opening where you stick the gas pump nozzle into? I noticed I don't have anyrhing there on the eclipse but my other vehicles I do

2001 Eclipse GT spyder 5-speed. Okay so I've started to get this really bad noise from the back of my car when I start it. This only happens after I start it up after driving for a while and the engine is completly warmed up. For example I would go to the store, and after shopping I would come...