Hey guys my car is making this vibrating noise from under the car. It sounds like its coming from the exhaust (canister). The used car place I got it from said that it was a heat shield that they tightened and re tightened, however it still makes that vibrating sound. It seems to only happen when the car sits for awhile. Like if i start it drive it and shut it off and start it up again to try to show someone it doesnt make the vibration sound. Does anyone know what this is or could be? Thanks!