I searched quite a bit on this but it seems like most cases vary from car to car. What I drive is a 2000 EX coupe with only 45k miles on it. The only mods I've ever done to the engine are an intake and a header. However, when I decided I was going to sell it soon, I took off the header and put the stock one back on.

Ever since about 3 weeks ago (~1 month after putting the stock header back on) there is a very noticable, loud rattling sound coming from somewhere. I'm fairly sure it's with the engine, but WHAT in the engine is what I'm trying to figure out.

- I took off the header head shield.. no dice
- I got the car up on a lift and tightened every single bolt with the exhaust system, especially the spring-bolts between the header and cat.
- One of the header brackets that I had bent back for the aftermarket header.. we bent back forward and bolted to the last section of the header.

The shop that I always go to (where I can use their lift, thank god) and I were sure it was that bracket. We set the car down, revved it to the 2600-3000 "threshold" and it was fine. 10 minutes later once my car warmed up again, the noise was back and continues to follow the same pattern.

What do I check next??

 

do u know where exactly the sound is coming from?

 

underneath the car.. it really sounds like two metal things slightly rubbing against eachother. it also seems to be right underneath the drivers seat (which is why i was inclined to check the header-cat connection). i dont think it's part of the cat-back.

i also bent back both dust shields on the front rotors... that wasn't it either.

 

u sure its comming from under the car?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by zoops &raquo;</TD></TR><TR><TD CLASS="quote">underneath the car.. it really sounds like two metal things slightly rubbing against eachother. it also seems to be right underneath the drivers seat (which is why i was inclined to check the header-cat connection). i dont think it's part of the cat-back.

i also bent back both dust shields on the front rotors... that wasn't it either.</TD></TR></TABLE>

"right under the seat", but there is nothing under the drivers seat.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1517cc sohcvtec &raquo;</TD></TR><TR><TD CLASS="quote">u sure its comming from under the car?</TD></TR></TABLE>

well the only other option i guess would be from the engine. while that may be possible.. i cant imagine something making such a god-awful sound between a small portion of rpms.. yet running perfectly great and strong throughout the rest of the entire rpm band. like i said, my car only has 45k miles and i consider it to be running in absolutely perfect condition... except for the noise.

if i have the windows up and any volume of music on, you really can't even hear it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by civic_type_r &raquo;</TD></TR><TR><TD CLASS="quote">"right under the seat", but there is nothing under the drivers seat.</TD></TR></TABLE>

well i know not directly under.. but that general area of the cat. i will probably check next to see if it is the heat shield on the cat.. but i don't want to have to take that off.

 

i have a feeling that is something is loose between the header and catyltic conv. U might need to change your catylic converter.

 

or some metal that u bend that is hitting with the other parts of exhaust system. Is it hanged properly is it nice and sturdy that it doesnt move.

 

the entire cat back exhaust is stock.. never been altered.. i tried to jiggle it around while it was on the lift, but nothing appeared loose with that.

when i get back to the shop on monday i'll check the cat heat shield, the cat itself, and ill go over all the connecting bolts again.

any other possibilities?

 

It could be your tranny or maybe your crankshaft but i seriously doubt that. im thinking it is you heat shield or the bracket where u hook on your header. yeah just check it out or just go to muffler shop i dont think they will charge that much. Good luck!

 

bump for any more suggestions.

thanks for the help civic_type_r!

 

If it's a stick, check the shift linkage.
Alghough you'd probably feel it on the handle, too.

 

yea it's a manual but i've never noticed any unusual vibration or probems while being in that rpm threshold at any time (neutral, shifting, cruising, accelerating, downshifting, etc...all normal)

 

what about the heat sheilds that are between the cat back and the car?? you might have loosed one during the swap and it just now started making noise????

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Project_DX &raquo;</TD></TR><TR><TD CLASS="quote">what about the heat sheilds that are between the cat back and the car?? you might have loosed one during the swap and it just now started making noise???? </TD></TR></TABLE>

well i didn't touch it during the swap (of the header).. but i'm certainly gonna check on that.

lunchtime bump before i put it up on the lift

 

Its possible that the baffling inside the catalytic converter has partially broken and is rattling inside the cat. My brother had this problem on his stock gsr cat and it only was noticeable at a certain rpm.

 

I've had the same problem on a few occassions. Most recently I thought it was my heat shields as it had been in the past but after removing two of them I decided to just tighten everything under the car and it was my down pipe.

Best of luck with that.

 

The donut gasket between the header and cat is probably not there or damaged.

 

it was the heat shield over the muffler that came loose

so much for thinking it was towards the front of the car..