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Old 06-03-2008, 09:27 PM   #1
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Strange exhaust noise when engine is hot

Hello all, this is my first time on this site and I need some help. I have a 2003 Boxster S (great car). It makes a buzzing rattling noise coming from the underside of the car on the passenger side. This noise seems to be coming from the exhaust pipes. It is especially worrisome and loud when I back off from the throttle at low speeds. I had the 'heat shield' tightened, but that did not fix the problem. Any incites as to what it is and how I can fix this problem. Regards. Compass1.

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Old 06-03-2008, 10:21 PM   #2
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Noise

CHECK ALL YOUR CLAMPS, AND SUPPORTING BRACE TO YOUR MUFFLER. LOTS OF NUTS THAT POTENTIALLY COME LOSE. Also CHECK THE LOOSENESS Of ANY ALUMINUM HEAT protection UNDER THE ENGINE. Does THE NOISE OCCUR UNDER NEUTRAl with just revving the engine? Or is it just when driving?
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Old 06-04-2008, 04:51 AM   #3
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The cats might be damaged.
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Old 06-04-2008, 04:58 AM   #4
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I had a rattle from my exhaust area only after the car warmed up. Turned out to be a loose clamp that connected a U-tube from my cat to the muffler. The U-tube would move slightly when I shook it. Tightened it up, and no more rattle.

When the car is cold, grab onto every single exhaust part and shake it to see if anything is loose. That's how I finally found out my problem.

It could be a bad cat converter, but not as likely IMO, because you would also probably get a CEL light if that were the case.
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Old 06-04-2008, 07:11 PM   #5
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Hate to be cynical, but I'd bet on a bad cat. It can be really difficult to isolate the rattle, I know from experience,and there are lots of ways to temporarily muffle it, but if its the cat the only permanent fix is a new one (and it's worth it). Good luck.
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Old 06-06-2008, 02:09 PM   #6
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Hey Compass1,

I had two areas of vibration similar to the one that you described. For the first one, I ended up putting a large screw-type hose clamp completely around the heatshield (re: after having tightened all possibilities to no avail) and that was able to do the trick.

The second vibration came from an aftermarket header that was abutting the variocam cover w/c I was able to creatively muffle using exhaust wrap and two screw-type hose clamps.

Good luck and let us know what you find.

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Old 07-28-2008, 01:14 PM   #7
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Broken Cats

I found out that the rear cats are broken on my 2003 Porsche Boxster S. The noise that is produced in and around the exhaust when the car gets hot is very loud. Porsche will not replace the broken cats on warrrenty because no failure report is made when the car is plugged into the diagnotic machine. Does anyone out there have suggestions for repair or replacement? Names of exhaust products and contacts in the US would be appreciated. Thanks, Richard
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Old 07-28-2008, 01:29 PM   #8
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I don't hear a rattle when I drive, but when I'm parked after a hard drive, or even a normal drive sometimes, there's a crackling noise from the exhaust area.

Is that normal ?
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Old 07-28-2008, 02:39 PM   #9
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Quote:
Originally Posted by nefarious986
I don't hear a rattle when I drive, but when I'm parked after a hard drive, or even a normal drive sometimes, there's a crackling noise from the exhaust area.

Is that normal ?
Yes, that's the exhaust, mainly the cats, cooling off. Metal expands when hot. Then starts to constrict during the cooling process.
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Old 07-28-2008, 02:45 PM   #10
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I had a such viration noise on my left cat, it was happening exactly at 1000 rpm (sometime at 2000 rpm).. finally a small solding tak fixed the vibration

get a rubber hammer and hit at different places until you can reproduce the sound
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Old 07-28-2008, 04:36 PM   #11
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Correct me if I'm wrong, but aren't the manufacturers required to certify emissions components for 80k? I had both cats replaced on my last BMW at 70k under warranty.

Patrick
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Old 07-28-2008, 04:52 PM   #12
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If you are positive the cats are bad, then I'd buy some salvaged ones from LA Dismantlers or Oklahoma Foreign.

However, your onboard computer would be telling you if anything was wrong with those cats.

My guess is that you have a small, loose piece that needs a whack or two with a hammer.

I had the same annoying vibration coming from the passenger side cat and got under the car when it was cold and start tapping on various things with the head of a screwdriver and found it was a heat shield (not the thin stuff, but a thick steel one).

So, I got back under there with a hammer and gave it a couple of good whacks and tapped on it again and heard nothing... so I took it out for a spin and that was the problem after all.

You should definitely try this or have an independent mechanic tap around for you if you don't have ramps or floor jacks.

Do let us know what the final solution is on this thread so others can learn year after year when they do thread searches.
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Old 07-28-2008, 05:22 PM   #13
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Originally Posted by bmwm750
Correct me if I'm wrong, but aren't the manufacturers required to certify emissions components for 80k? I had both cats replaced on my last BMW at 70k under warranty.

Patrick
Exactly, this should be covererd by warranty if the cats are in fact bad.
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Old 07-28-2008, 08:13 PM   #14
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The cats aren't technically bad if they pass emissions, even though the rattle indicates they are beginning to break down. The noise is annoying for sure, but it's probably not possible to get the manufacturer to warranty them unless they fail the emissions test. Good luck.
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Old 08-06-2008, 12:47 PM   #15
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I've got a set of brand new Stebro Racing secondary cat bypass pipes available... PM if interested... Thanks

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