On my 91 the stock heatshield on the downpipe made alot of noise. On my 99 i put in the roadster sport midpipe, with a cat, and the welds on the cat are shite, And they rattle like sin. I have shoved little pieces of high temp rubber in between the can and its shield which remedied the problem....for 3 days. Now it rattles somewhere else on the cat's heat sheild. My next move is to......trade it for a mazdaspeed. But if I was not going to do that, I would take the heat shield off of the cat, or delete the cat.