I have the old jeep rattling exhaust. It sounds like thin metal shaking under the car, or some rocks in a coffee can, the sound is coming under the passanger seat. I was living fine with the noise, only happens sometimes on idle, and when accelerating at around 1500rmps. Someone told me today that it sounded like my jeep was going to fall apart so it kinda made me concern. If your living with the same rattle, how long has it been like that?