wtf is doing that? the rubber parts are holding the cat stiff...i wonder if theres a rock trapped or something.

 

the cat may be breaking up inside.

 

Look for a pebble trapped between the heat shield and the cat itself. OEM cats usually age well, but I did have an aftermarket one fail on my Miata. Tapping the cat with a hammer produced a rattle. The brick actually broke free and rotated 90 degrees. The car didn't run so well like that.

 

does it rattle worse with higher rpms?

 

I don't know if it's true for all civics, but
My '97 civic HB (DX) muffler and the cat heat shield rusted off last two years ago,
My dads '97 civic Sedan (LX) muffler and mid section rusted off last year,
My friends '98 civic HB (CX) mid section rusted off a little over a year ago
and another friends '97 civic Coupe (EX) muffler fell off in a middle of a highway, almost at the same time.
All those were OEM parts and all of us (except for my dad) have replaced them with stainless steel. You should do the same and save yourself the anguish.

 

umm try searching the articles on http://www.hybridgarage.com its got a incident where the cat was making a weird sound because it was flowing too well....so you might wanna check that out

 

i don't think it's your cat... did you check the heatshield? I'm pretty sure that's the problem, it usually is.

 

yep I agree, it looks like all honda heatshields are bound to have the same problem. The heatshield covers the cat. My OEM one rattled and was removed after months of that noisy embarassing sound. Now I just installed a new exhaust with after market cat. 5months later I hear a new rattle, I'm about to go nuts.. with this heat shield thing.

 

exhaust is rusty or sumtin

 

my heat shields started to rattle after i scraped them over to many speed bumps and driveways. so i took them off today and the rattle went away.