I have a 00 Accord LX with 115k miles on it and the car runs great, but when I hit the gas pedal just slightly you'll hear a rattle noise from under the car. It won't make any noise if you step on the gas pedal hard... just when you slowly step on it you'll hear it anywhere from 1.5k to 2.5k rpm then it goes away. I thought it was the heat shield and so I went under the car to see that all the bolts were there and in one piece. I had some clamps at home so I went ahead and clamped the front and rear of the heat shield and still I hear the noise. I removed the clamps and the heat shield and still the rattle! I go under the car and I hit the cat so it shakes and I can hear the rattle noise coming from the cat itself. Anyone know what is causing the rattling noise inside the cat? I was thinking about maybe clamping the cat onto something so it wouldnt shake and make the noise, but I didn't want to mess with anything down there until I got some advice. Any help would be great... TIA!!

 

when the cat starts going bad it breaks apart internally, that could be whats happening

 

Is it something that needs to be replaced and is it a diy type of job? Thanks!

 

You can buy a cat and replace it yourself but it would be best to just have an exhaust shop do it. Call around to get the best price.

 

On my 92, Honda used a double-walled downpipe with an air gap as a way to insulate the pipe without using external heat shields. Mine made a terrible rattling noise and it was impossible to find, eventually i saw that there was impact damage that caused the inner and outer pipe walls to squish together.

Just a thought in case you can't locate the issue. The aftermarket pipes AFAIK are all single wall.