Mine also rattles at idle.

 

+1
I was just under my car today installing a mid-pipe and found that my rattle was from a broken weld on the heat shield.

 

I'll get under mine tomorrow. I find it odd that the rattle also happens when I close my trunk.... That tells me whatever is loose, is in the back half of my car.
My initial though was something on the RP supercat but now I'm thinking the heatshield

 

Would it be stupid to ask where the heat sheild is?

 

Well kind of. It is the metal shield that rests above the exhaust.

 

Then I'm not going to be the idiot who asks then.

 

its right where the catback mufflers sits.

 

My rattling heat shield is above where the cat would be.

 

Your mathmatical reasonabilty is beyond the dark force.

 

Just use the force Luke.

It will weld the exaust shield.

 

Update! Guys I took my car to Rick's Rotary Performance today and they found the problem. It is not the exhaust heat shield, but the heat shield for the catalyic converter. I will be taking it to Mazda to get it fixed under warranty. Rick's told me it needed to be re-welded or replaced. If your exhaust heatshield isn't the problem, check the one for the cat. That is probably the one causing the problem. It is pretty bad Mazda couldn't find the problem even when I said it was the heatshield. They should know the most about their own car.

 

First post sadly had to be a problem :/ ... anywho this is what I believe my problem is as the hangers look fine and don't appear to be touching anything. I will have another look tomorrow to see about the heat shields. None the less I will be taking my 8 into the dealer on Monday to see if they can pinpoint the issue. Oh well if its the cat .... guess its time to get that high flow cat and well might as well get the greddy sp2 while I'm at it.

Thanks for all the useful info in the thread!

 

One common rattle is the hanger that nearly touches the passenger side of the differential....

Also check the big heatshield on top of the muffler - a real rattler!

 

It isn't my exhaust heatshield or the hangers. I took it to a shop when I got my 30k serivce done and they said it was the heatshield on the cat that was loose. I believe him because he owns the shop and also has an AT Rx8. This guy is very honest and said I would have to take it to the dealer. So I took it to the dealer and the stupid *** tech said he couldn't find the issue. They said he banged on the cat and found nothing. I went back a few hours later and showed the service manager, who I knows me well, and I was able to show him exactly how it occurs. It happens when I shift from park to reverse or drive. Also when I am in reverse and back up slowly. Another time is when I am idling at a light I hear the thing vibrating and you can feel the back end shake through the seat. The service manager said it may be somthing with the tranny, which I agreed with in the first place. He said they would check and see if any more AT Rx8's had this issue because he thinks it could be normal since mine is getting up there in mileage, 40k miles, or there actually might be something wrong. I may bring it back Wednesday and see if they can get this solved.

The cat dying actually makes total sense since it does sound like there are pieces flying around.

 

did anyone find out what happened with this? i have same issue....

Is it the cat heatshield in the end?

 

This ended up being my catalytic converter. The thing needed to be replaced. If when you accelerate quickly or stop quickly and you hear what sounds like pieces moving around through your exhaust, it's your cat.

Good thing is Mazda covers cats until 80k. WOOT!

 

I actually fixed this a few months back. Found out it was that one of the exhaust hanger was to close to the diff. I took a set of large vice grip pliers and pulled the hanger away from the diff. This finally fixed my problem. No more rattle at idle!