1998 Pontiac Sexfire. Similar to a sunfire but different. Today there was sound coming from the right front of the car, not sure where from exactly. It sounded like there was something knocking around in a steel pipe or something, like hitting the walls. It only made the noise when i let off the gas pedal, under braking it was fine, under acceleration it was fine, pushing the clutch in didnt affect anything. So.....What could be the problem?