Well I thought I had isolated my exhaust rattle to a failing Catalytic converter so I replaced it today. What I found in the old Converter intrigued me. The porcelain appears fine but I found 3 peices of metal. They seem to form what appears to be (for lack of a better description) a really deep unmbrella stamped out of steel and about 1/2" wide by 1" deep. To me it looks like some sort of shield for the O2 sensor. I have not replaced the one on this car, is my presumption about these peices of metal correct? Now the bad news, the rattle remains but has moved to a lower RPM (2200 or so) and sounds about the same. I am hoping that these are litle peices of the O2 sensor and maybe they are in the big main muffler also (and I can shake them out). By the way, the 02 sensor is only 15,000 miles old. Sorry its so long and thanks for any replies.