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Old 06-17-2012, 09:11 PM   #1
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Rattling Noise from Catalyetic Converts - advice needed

I took my 01' Boxster S in to a local independent shop the other day for an oil change. Asked to check on a sort of rattling sound I was hearing from the back of the car. Was hoping it was just a loose heat shield, but alas it appears the rattling is coming from the catalytic converters...specifically the rear "secondary cats".

I have a few questions about this that I was hoping someone with more knowledge than me might be able to shed some light on.

First, what would be causing the rattling?

Second, is the rattling a sign that the converter has already completely failed, about to fail, or is it operating at reduced capacity?

Lastly, what would happen if it does fail completely? Is there risk of damage to other components, or will it just not process the exhaust up to emissions standards.

Regarding the last question, I know this is going to be a pricey repair and money is tight at the moment. Unfortunately, this car is also my sole daily driver so I don't have the option to just not use it for a little while. I can live with the rattle for a while so long as I'm not risking damage to other systems.

Any advice would be greatly appreciated.

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Old 06-18-2012, 03:00 AM   #2
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Sometimes the rattle is the disintegration of metal internally, in such cases replacement or rattle acceptance is the only option. Option two is only good in non smog test states as the converter is likely working at low efficiency if at all.
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Old 06-18-2012, 09:55 AM   #3
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I had the honeycomb come loose once on a Cherokee I owned.... it rattled around for years. Eventually, it disintegrated and tumbled until it assumed the shape of a ball and plugged the exhaust outlet, lol. Then I caved in and bought a new cat.
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Old 06-18-2012, 11:19 AM   #4
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I had the same issue. Replaced my 2ndry cats with some aftermarket bypass pipes and now the rattle is gone and the car sounds much better! Those cats are not part of the emissions control loop, so they should not affect smog tests- YMMV.
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Old 06-18-2012, 03:45 PM   #5
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You need to get under the car with a hammer and start tapping around. I had this same rattle and it was a clamp vibrating... A couple of good whacks with the hammer not only felt satisfying, it silenced the rattle.
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Old 06-18-2012, 05:22 PM   #6
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Did you remove the exhaust heat shield? Small pebbles get caught in the heat shield and rattle around. I took mine off... Rattle noise gone.
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Old 06-22-2012, 05:32 PM   #7
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Hello Saxster! I have an 01 S as well...mine has an odd rattle, you can only hear it with the top down. It also rattles on startup. My indy diagnosed it as the R/S forward manifold....about $600 to repair. That might be a good thing to check.

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