more rattling, not O2 sensor or exhaust.. ideas?

Eldorado · 07-30-2005, 08:42 PM

well when i bought the car it rattled.
I took it to Midas, borrowed their lift... lifted it up and banged around and found the culprit to be a loose o2 sensor... tightened it down and it sounded great...

drove it for about 2 or 3 weeks sounding good... and as you may or may not remember from a previous post of mine, I had a small emergency that required me to drive the car hard to get a friend of mine somewhere.... after i got back home that night, the rattling came back... or should I say *a* rattling was heard..

i assumed it was the o2 sensor and didn't think anything of it until yesterday when i took it back to Midas to steal their lift... hoisted it up and went to tighten the sensor... it was still firmly in place...

i banged around the entire exhaust system under the car hoping to find a loose clamp or something - nothing.. it was all fairly solid..

so my question to you is this..... if it's not the o2 sensor, and it's not any (noticable) clamp or part of the exhaust... then what could it be?

if it helps, it doesn't do it when the car is first started... it idles quietly... then you drive it for a minute or two, it starts... and THEN it does it at idle...

it gets worse the harder you drive it...

ANY ideas? it sounds like it's coming from under the car..

Moneyguy1 · 07-30-2005, 10:42 PM

Try the heat shields.

carsonmx114 · 07-31-2005, 11:51 AM

does your car have a converter on it? i've seen the insides of the converter break apart and rattle around.

Eldorado · 08-01-2005, 12:46 AM

hmm...
it does, and that's exactly where it sounds like it's coming from too... but it's an aftermarket cat that one of the PO's put on...

I'll give that a good shake and see what's what... i didn't even think that it'd be coming from inside the cat... i just got it lodged in my mind that it was a sound coming form somewhere externally because it was so loud..

Rmills944 · 08-01-2005, 09:01 AM

I had the flange on the cat rattling against the torque tube for a while. You may just have to grind the little ear off that flange and it should work fine if that's an issue.

pokey · 08-01-2005, 11:03 AM

Shaking it when it's cold, you probably won't hear a rattle. The casing expands as it heats up, causing the matrix inside to become loose, the harder you drive, the hotter the cat will get. Thus, worse rattling.

HY M8NC · 08-02-2005, 06:22 AM

I agree with MOneyguy...I had a rattle, and found that the rear heat shield had cracked and the two sides were banging together...

Eldorado · 08:44 AM

but if it were the heat shield that was cracked.. or a bracket was broken off.... it would do it right away after starting, right?

with this... I can be at a drivethrough... being right next to a wall i can hear it horribly... while I'm waiting for food, I'll turn my car off for the minute or so.... and when i turn it back on the rattling is gone, only until i drive out of the parking lot then it's back again...

very strange...

carsonmx114 · 08-02-2005, 06:37 PM

i have a 94 suburban and the problem you describe is just like what happen to it. drive-throughs were where it was most noticable.

Eldorado · 08-02-2005, 09:31 PM

[insert part where you tell me how you fixed the problem, carsonmx

]

carsonmx114 · 08-03-2005, 03:06 PM

i live in alabama, i just cut it off and put a pipe in it's place. i'm going to replace it though, it's to loud now and it stinks when it's idleing. you may know, but the inside of the cat is a honeycomb ceramic that gets red hot when the engine is running to burn off any unburned exhaust, this ceramic material sometimes breaks apart and that's what rattles around. most aftermarket cats have pellets in them instead so i don't know how well they will flow. if your cat's broken apart inside it will have to be replaced, or i have seen people take them off and break the ceramic completly out to make it hollow. anything short of replacement may be a problem for you if your state has emission tests.

Eldorado · 08-04-2005, 05:48 PM

being in canada, my car is over 20 years old, exempting it from emission tests.

what would me breaking the insides of the cat out benefit me? would it take away the loud sound? probably not the smell...

Techno Duck · Techno Duck's Garage

Had a rattle on my old 924S that was tough to locate, i ended up finding it by chance one day. Two different exhaust shops couldnt figure out what it was. Ended up being the exhaust manifold nuts that bolt the flange to the block were loose (two of them) causing a very annoying rattle. Worth a shot checking.

carsonmx114 · 08-04-2005, 07:25 PM

by breaking the insides of the cat the rest of the way out you will be knocking the pieces that are rattling around out, so you will have a hollow pipe left. if your car is exempt from emision you could have a muffler shop install a piece of straight pipe in place of your cat. the only advantage to hollowing out the cat is you have the apearance of having a cat on the car, since your exempt it would be less trouble and less expense to just remove it altogether.

Eldorado · 08-04-2005, 09:41 PM

hehe.. carson, got another semi-active thread already going on talking about just that