there is something rattling under my car everytime i accelerate. it's only gotten worse (to the point that everytime i press the gas it rattles). the rattling doesnt happen after 3000 rpm, but will happen anytime under. i think its the cat converter, cause i changed my exhaust a few months ago to fix the same rattling sounds, but its come back. when i changed my exhaust i didnt change the cat converter, so maybe thats busted or something? by the way, i have a 2.3 auto...

 

i had a similar problem and it turned out to be my exhaust shield or something like that was lose. either way it was a minor issue. i had it fixed for free.

 

I had the exact same problem. My exhaust heat shield was lose and that caused the rattling and the noise was intensified because I had rocks along the piping in the shield. It was also becuase the flexpipe was rotting. After I got my exhaust installed, the rattling went away.

 

Its the heat shield.

 

where is this exhaust heat sheild located. I have the same rattling as described above also but I've had everything in my exhaust replaced including headers, cat, custom exhaust and muffler. When I had the car up on the air lift when I had my crank pulley installed we check the exhaust to see if it was in contact with any other parts of the car and we also checked the hangers that hold the exhaust in place for rotted rubber but we didin't see anything wrong. I just figured that since the exhaust was louder than it was causing things to rattle now that didn't rattle before. Like when you put a big subwoofer in your car you get a bunch of new rattles because of the louder noise. BTW I have a 3.0.

 

in my old galant, i had a bad rattle and finally figured out it was the heat shield.
it was 90% rusted off and just banging around.
look under there and stuff to see if it moves

 

https://acurazine.com/forums/showthread.php?t=183977

im going through the same problem. im not thinking my exhaust hangers are loose causing the piping to move and rub up against the heatshields.

 

If it's under the car, it's the heatshield over your catalytic convertor, mine is tied up with a wire hanger, but when i replace my exhaust it's comin off.