Nasty evil rattle at idle / low RPMs

[Alpha.kx]

My civic has a nasty rattle that only really happens under two scenarios:

1. Car idles at around 500 - 600 RPM, when it goes below 1000 RPM on the idle, this is usually when the rattle starts

2. Low RPM at a low speed in a higher gear. If I'm at.. say, 25 MPH in third, I might hear a little rattle when the the car fights to get a little gas.

In both situations, when the car is happy with the amount of fuel it's getting and stops idling, it's totally fine.

Any thoughts on this? Unfortunately this developed only after adding DC 4-2-1 headers and a Megan high-flow cat

 

[TiiM iiS l3eAsT]

loose bolt maybe somewhere on exhaust system??....find where the sound is coming from...

 

[TaNk00VsM]

you know what i kinda have the same problem...but my car idles kind of low...mine sounds like the cat is hitting the heat shield thats around it but i havent confrimed it yet

 

[stolibears]

I too have the same issue. I have the DC header and a powercore high flow cat. I've had my honda mech. check for loose bolts and such without luck. The highflow cat. does have a little material inside unlike some of the straight pipes and I'm almost convinced that the insides have come loose and are rattling inside the cat. Kinda sounds like a couple of nuts and bolts in a coffee can.

 

[31dev31]

Mine rattles....no exhaust modifications.... typical honda...

 

[Esotericimage]

My 4-1 header used to have a rattle, it was cause the pipes were too close together... after i went boost, it went away.

 

[Gonzo]

Heatsheilds on a honda are worthless..they will rattle after a while and theres not really a way to stop them once they start so i just took mine off. as far as the OP..where is the rattle coming from exactly? be more detailed.