I have a 2002 C2 with an exhaust rattle at 1200-2000 RPMS. This is extremely irritating.

Here is what I have eliminated:

1. It's not the cats, because the car has no cats, just some beautiful polished stainless straight pipes that are not rusted, loose or cracked.
2. Not a loose bolt or nut, have checked every single bolt, nut and washer from the headers to the mufflers and on the straight pipes.
3. Not the brackets that hold the cats to the subframe. I thought for sure that this is what it would be, but I took the brackets off completely tonight, then started the car up and the rattle is still there.
4. It shouldn't be the mufflers because they are brand new FABSPEED mufflers with less than 1000km on them.
5. The clamps that hold the straight pipes to the muffler pipes were suspect, but they've been tightened and I also put a bead of gasket sealer around them.
6. It's not an O2 sensor, all of my O2 sensors are nice and tight.

It definitely has something to do with the exhaust. Exhaust was nice and rattle free for the first 500 km or so, then various rattles started and I was able to resolve most of them. It basically sounds like an clamp is loose and rattling, but this possibility has been painstakingly eliminated. I've gotten up and under there checking for metal-on-metal contact and NOTHING is rubbing up against any of the exhaust pipes.

This sound is ruining the experience of driving a perfectly good car. Any suggestions on what else I should be checking?

 

Loose tips are pretty common. Have you checked them?

 

The tips are the only things I have not checked. They are aftermarket dual tips. Would they usually be rattling at the upper circular flange, or somewhere near the tip itself? I wonder if I can test for it without someone else helping.

 

I think they typically rattle at the flange.

Try tapping your exhaust pipe with a rubber mallet and see what you can find.

 

I had the same issue. It was 1 missing bolt that connected a bracket to the frame. Easy $1 fix...just bought a bolt.

I think when I was getting my exaust done it was never reinstalled. There was about 1/8" gap between the 2 pieces of metal where the bolt was missing that caused the rattling. I screwed in the bolt and problem fixed.

I thought it was the tips for the longest time until I triple checked.

Just get under you car with a flashlight and make sure all the hardware is in place and if it is, repeat the same process with the car running and try to pinpoint the noise.

 

I removed the bracket that holds the straight pipes to the frame entirely last weekend just to see if that was the source of the sound. The sound continued even with the entire bracket removed, so the sound isn't coming from there. I'm guessing it's the tips because the clamps were rusted to hell when I last removed them, and the tips are aftermarket.

With no cats, it's kind of hard to start the car and then sit under it tapping away looking for the sound. If you've ever been behind a completely cat-less 911, you'll know what I mean, the fumes are toxic =)

 

Bump. This is getting to the point where I'm going to scrap this car if I cannot locate the rattle. Well, not really, but I'm going to have to take it in and pay someone $200 an hour to track down the rattle. This thing rattles so noticably that I probably wouldn't be able to sell the car as is, if I wanted to.

I have now replaced the exhaust tip clamps and tightened both exhaust tips to no avail whatsoever.

What has been done so far:

-Replaced cats with straight pipes, full stainless, new gaskets, new bolts, new nuts, new washers, less than 500 miles on them, all checked and re-checked and tightened.

-Replaced OEM mufflers with fabspeed mufflers. New gaskets, new bolts, new clamps. All tightened, checked and then rechecked. Less than 500 miles.

-Replaced OEM exhaust tips with high quality aftermarket tips, tightened, checked, and rechecked for rattles.

-Finally replaced the circular clamps that hold the lower pipes (tips etc) to the muffler output pipes. They were rusted. I was almost 100% sure that this is where the rattle was coming from because this was the ONLY remaining part of the OEM exhaust that hadn't been replaced (Yes, it even has new headers!). Made sure these new clamps were nice and tight today.

-Checked the clamps that hold the cats to the mounting bracket on the motor, tightened them. Started the car up and it still rattled, so I removed the clamps entirely (*temporarily) to eliminate them as a possibility. Still rattled even without clamps.

-Checked all exhaust piping to see if any rubbing contact was occurring. Nothing, all pipes etc are free and clear, and come nowhere near rubbing anything.

-Thought it might be a loose O2 sensor, tightened both just to be sure.

-Tapped the pipes with a rubber mallet, nothing.

I now have a 100% new full stainless exhaust system from the the headers to the tips. This is driving me nuts.

It sounds exactly how a loose exhaust clamp would sound if it were rattling around the pipping. It is definitely an external sound, it is not coming from inside of the motor itself. If it were any other car, the first thing I'd be checking would be a loose aluminum heat shield. It sounds like a thin aluminum shield is rattling somewhere, or an exhaust bracket. I've worked on cars for years and years and this type of sound has only ever been produced by the above two problems. It is not coming from inside the engine bay, it's coming from UNDER the car, in the outside engine/transmission area.

It ONLY makes the sound from 1,500 to 2500 rpms. The sound is loud enough to be heard over the catless full exhaust system. We live on the 14th floor of an apartment building, and my wife can hear me come home from blocks away because the rattle sound reverberates off of all the buildings in our neighborhood.

Any further suggestions highly appreciated before I bite the bullet and take it to someone. Roads are pretty poor here and my suspension is stiff. Is there any heat shield or other clamp somewhere that might come loose and make such a sound?

 

Maybe your heat shields? I had this happen to mine.

 

You said you replaced the mufflers with Fabspeed and all was well for the first 500 km or so. If you've checked all that you said you have I would have to take a logical guess that it's a muffler gone bad.

 

I had a broken exhaust hanger bracket once that caused a bad rattle.

 

heat shield is my guess, it gives off the sound of a loose clamp etc. If you have taped the exhaust and didn't hear anything then it probably isn't the exhaust. It is something around the exhaust that is making the noise. I have Fabspeed also and a couple times already my 0s sensors came loose and the noise was so annoying. Take the rubber malet and tap on anything under that car thast can possibly rattle.

 

Problem was located last weekend. It was a loose O2 sensor simulator. It was hand tight when the car was parked and cool, but after warming up a little, it would rattle around. A quick turn of the wrench and now it's all good!

 

Thank you for following up! Where is the O2 sensor simulator? Never heard of it. Near the sensor?

 

No, my car is running straight pipes instead of cats, so there are two little simulator plugs that go where the 02 sensor plugs would usually go. If you aren't catless, you won't have any O2 simulators, they are aftermarket parts to avoid triggering a check engine light on a catless 996.

Anyway, in your case, check the o2 sensors themselves.