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.

what happens if you disconnect the system to the rear of the cat? If it continues would it be safe to say it is not in the muffler? I have had the experience of confusing a rattle for a small leak in the system. good luck