Hello,

Yes I solved it, sort of. First I found a good test to check for "rattling cats": What you do is hit each cat with a rubber mallet. This will tell you if one is bad (It will make a rattling noise). I had one bad and one good. It was a whole assembly so I changed it. This helped quite a bit, but I thought the source of the rattling was still there and the cat was just "sympathetic" rattling. However, a couple of years down the road and it seems all the rattling is gone. I had also tested my knock sensor which was working fine.

Anyway, tap on your cats (with the car NOT running), and see if you can hear any rattling noise. What happens is the insides come apart for whatever reason.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra