Resonating rattle at idle - where are the heatshields?

[Conor D]

I've got a rattle coming from the underside of the car, it sounds like it's coming from the middle section of the exhaust. At idle it will rattle, but if I put on the A/C at idle it doesn't as the revs rise.

I think I've been hearing it as I drive too, but I'm not sure if it's just in my head.. Are there heatshields around the middle section of the exhaust that it could be rattling against?

[B3njamin]

I can't help but I have a similar issue by the sounds of things - would be interested in hearing some ideas.

[Roger Dodger]

I had one which happened on over-run, and when holding steady at 3k-ish revs (when in gear).

Turned out to be the cat.

[Dan_1981]

Had the same thing - turned out to be the outer casing on the cat - i "removed" it.

Problem solved.

[B3njamin]

Top work lads will take a look tomorrow and check around the cat.

[Conor D]

I climbed in under the car today and had a look, I took a video:

http://www.youtube.com/watch?v=AOPHKIEhTmg

If I hold a piece of wood to it, it stops the rattle a bit.

[Oldandslow]

Sounds internal to me. Are the thin metal covers loose or still solidly attached? The heatshield was more of a buzzing on mine, I tied each end up with garden wire to force the clamshell halfs together.

The cat nuts are a bugger to get off. I plus gassed it for 24hrs with repeated applications and still needed a big breaker bar to shift them and broke 2 of the studs in the process. If it's a pre 93 import I think you can fit a cat bypass with no problem for MOT. Emissions seem to be OK, my cat has no internals and never had an issue.

[Roger Dodger]

Looks like a new cat is needed (can't see the heatshield on yours...) I might be being blind!

[Conor D]

Roger Dodger said:

Looks like a new cat is needed (can't see the heatshield on yours...) I might be being blind!

Looking again, and looking at some of the other cats it seems as if mine is one solid piece with no visable heatshield?

[Dan_1981]

This is what mine looked like a few months ago

http://www.pistonheads.com/gassing/topic.asp?h=0&a... Issues......&mid=169273

[Roger Dodger]

Conor D said:

Roger Dodger said:

Looks like a new cat is needed (can't see the heatshield on yours...) I might be being blind!

Looking again, and looking at some of the other cats it seems as if mine is one solid piece with no visable heatshield?

I think (could be wrong), mine had a separate looking shield. Your's looks like your touching the wood on the cat.

Good thing is that I got a newish 2nd hand cat for £80.

If you end up fitting one yourself - BE CAREFUL WITH GASKETS. Don't put one before the cat, parts of it can breakoff and burn through the cat over time - shortening its life.

There may be someting else you should do - I can't remember, someone on here may be able to add more info.

[Conor D]

Hmm, I guess it's a good possibility that it is the cat then.

I'll have to take another look tomorrow just incase it could be the heatsheild above the cat.

Is there any way to test the cat, such as tapping on it? Or is there any quick way to stop the rattle; such as bashing out the internals?

Time to look at a de-cat pipe I guess..

[Roger Dodger]

I don't know about bashing it out (fnarr fnarr!), when I looked in mine it was a really dense honeycomb - which looked fine, part of it (don't know what part) was fked.

I don't know if I'd want to bash it out and risk bits flowing through the system.