On my 00 dx, there is a metallic noise like something is hitting that takes place about 8 times a second, and only happens when moving slowly or fast accelaration. I took the front tire off and my friend got under, he doesn't think its the shielding around the cat, but the cat itself has loose material inside. The shielding is above the cat inbetween it and the underside of the car, not underneath it. What can I do about this, should I try to cut away some of the shielding anyway or could it cause problems?