So I recently about 2 weeks ago ended up buying a 04 rx8 6 speed. The car has 73,000 miles on it and is still under the dealers warranty. I had no issues with the car until today when I got back from about a 30 mile drive home from work I start to hear some rattling. Not sure what it was a pulled into a parking lot put the car in neutral and gave it gas. You dont hear the rattle while the car is idling but the second you give it gas and it passes like 1000 rpms you hear the rattle til about 4000 rpms where I think the noise of the engine just drowns it out. My buddy thinks it is loose exhaust or something. Im not sure but its starting to drive me crazy. Very hard where to tell the sound is coming from but it sounds more under the car. Best way to describe it is a rattle/clinking kinda like if someone put a bolt in a tin pan and made it vibrate.

 

Could perhaps be part of your cat breaking up and is getting stuck in the exhaust. Had something very similar with a Range Rover, I just revved the *** off the car until the bits came shooting out the exhaust... and about 20 foot across the road!

 

Check your cat. If cat is bad you need to replace it or remove it. Do not drive the car with a bad cat as it may cause serious engine damage. There are a few different ways to check your cat. You may pull it out and look inside. If the material is broken, your cat is bad. You could also look underneath the car after a hard drive. If your cat glows red then it is bad (you got to be in a complete dark area to do this). You could just take it to a dealer and ask them to pull it out and inspect it. Cat's have a 8 year/80,000 miles warranty so you still might be covered.

 

Dude if it's a clinking sound, yes look under the car at the cat. However, it's much more likely to be the heat sheild surrounding the cat rather than the internal catalyst components itself. This is good, much easier/cheaper to fix. Search for fixing cat heat shield noise with hose clamps

 

Thanks guys. Yeah im hoping its just the heat shield. Im gonna go out and take a look in a bit here. I have a appointment at mazda in 2 days so if I cant get it figured out they can prolly figure it out.