I noticed when i'm goin 65+ i hear a small vibrating "wiggling" noise coming from under the center of the back seat. I've made sure nothing's loose inside the car. I also hear the same noise from under the car in that spot when in park, but not as loud. (i can't hear it from in the car at speeds lower than 50ish) it sounds like tin foil being ruffled by wind. Is this somethin to do with the fuel line there? Its in the right spot. Any ideas?

 

Check your exhaust system.