rattling under car

[predator_96817]

ok, so recently i've been hearing a rattling sound. my friend stuck his head out the window and says it sounds like its coming from the middle of the car. it doesnt sound like heatshield from cats, its not that high pitched, but I do scrape my exhaust a lot of bumps and stuff. i dont know exactly when it started rattling but i didnt do anything to my car in the past year, except change the oil(oil level is ok). it comes at low rpms(1300) and higher. i dont hear it in neutral, only driving, but ill double check that.
i bought some contact cleaner at radio shack and sprayed my maf, thinking it was detonation and put some NOS octane booster(hard for me to get racing gas), but after my friend said it sounded like middle, maybe its not detonation.
Any ideas?

 

[Kilgore Trout]

cats

 

[predator_96817]

cats? I hope you are right, that would be an easy fix. just outta curiosity, wouldnt i hear it in neutral though?

 

[DocG]

I learned a few things about rattles when I was battling something like this.

Crawl under and check the shields on your cats. It could be your actual cats that are bad....what year and how many miles on your car? If you hit the exhaust a lot, it can break up the stuff inside the cats. But I'd think you'd hear it in neutral too.

Is your car a manual tranny? If so, there's a metal plate that is attached where the clutch cable and bracket are on the tranny. From what I've seen, this is usually just attached with one bolt, meaning it is prone to loosen and rattle.

Are you sure its coming from the middle and not from under the hood? Sounds can be very hard to pinpoint, especially if its doing it while you're driving. Many sounds will bounce off the hood back towards underneath....making it sound like its coming from underneath your car when it could actually be coming from your valves or something.

Worse case scenario, you could have a valve rattling or a piston slapping. Not likely, but might be worth listening with a stethoscope to each cylinder.....or unplugging the coil for each cylinder to see if you can stop the rattle. Check to make sure all your plugs are tight too.

 

[predator_96817]

car only has 23000 miles but the cats are catco brand, i heard they suck. if it were the valves or pistons, would i hear them in neutral too? btw, its an auto. another thing i should note maybe, is that in the cold mornings, i see white smoke coming out the left rear tail pipe, but not the right. im pretty sure its not oil or coolant, just smells kinda rich. another bad cat clue?

 

[DocG]

I'd think if your cats were that bad causing smoke, you'd have tripped a CEL for an O2 sensor giving bad readings.

Someone correct me if wrong.....but don't bad cats smell like sulfur?

If its a noise that only happens in gear and while driving....its probably something that is affected by load. I still would think that a rattling cat would rattle in neutral too since the rattling is probably more of the pressure of the exhaust passing through rather than anything related to being in gear.

 

[Blue04Mach1]

He's right about the cats setting off MILs....or an 02 sensor....Does it make a ticking sound when your rolling with the car off? its very hard to pinpoint on an automatic...but in a 5pd many times its the bolts connecting the UV joints to the driveshaft....rattles like crazy and will make the whole car rumble on the highway.

 

[Blue04Mach1]

The smoke coming out the tailpipe is normal if it isn't thick...why only one I dont know without looking under your car..stock exhuast system?

 

[DCjuggalo]

does it sound like a empty can of spray paint?

only does it when your barely pressing the gas?

 

[predator_96817]

ok, i found out it does do it in neutral...just not as loud. Then on the way home, i heard it on deceleration(70% sure). i stuck my head under the car while trying to press the gas and it sound like its coming from cats(but that could be my mind really wanting it to be). RPMs dont really matter. bassani x with catco cats wielded in and borla stinger cat back. so..cats?

 

[StickShift84]

I had the same problem about 2 years ago, I also had catco cats. I removed one of them and there were big chunks of the ceramic material inside that were rattling aroung, there was also a big piece stuck in the exhust pipes further down from the cat. I replaced the whole system with a pypes x- pipe w/out cats and a magnapack catback. I have never looked back.

Catco = POS !!!

 

[predator_96817]

cool, thanks for the info dudes! hell, maybe ill get some headers while im at it

 

[GDawg]

Also check the dust shields on your front disk brakes. The rivits sometimes break.