rattle at 5 to 5,500 rpm

**Justin93** · 07-15-2008, 03:29 PM

Ok I took the car out for a speed run today and when I get on it, at about 4,500 to 5,500 rpms it makes a funny rattle noise. When I race 5,500 is usually right where I shift. Could my new K&N fipk have caused this? Just wondering as I didnt notice it before with the stock air intake and silencer. I checked all the mounting hardware and its all tite. Also the cat was replaced under warranty last week, could the flange have come loose between the cat and head pipe and require a retorque since it doesnt use springs? anyone got any clues?

Thanks
Justin

**0rion** · 07-15-2008, 11:39 PM

does it sound like it's coming from the engine compartment or under the car? It could be something as minor as a loose bracket or something along those lines but it could also be detonation or "ping".

**qwkgto** · 07-16-2008, 02:53 AM

Originally Posted by Justin93

Ok I took the car out for a speed run today and when I get on it, at about 4,500 to 5,500 rpms it makes a funny rattle noise. When I race 5,500 is usually right where I shift. Could my new K&N fipk have caused this? Just wondering as I didnt notice it before with the stock air intake and silencer. I checked all the mounting hardware and its all tite. Also the cat was replaced under warranty last week, could the flange have come loose between the cat and head pipe and require a retorque since it doesnt use springs? anyone got any clues?

Thanks
Justin

sounds like detonation,maybe the air flow of the new cia did it ,jack the car up ,hit them cats with a dead blow hammer if they rattle,tighten em,id call it not the cats because it would rattle all the time not at peak hp.what octain and or gas you run in the car,stick a bottle of 106 and or some other good octain booster to see if it still does it..the aluminum ls motor sounds like a very slight rattle when they are detonating,I advise you to be very carefull, dont take a lot to break em.let us know what you find.

**Justin93** · 07-16-2008, 10:23 AM

Since I've bought the car Ive been putting nothing but 92 or 93 depending on the gas station . Its weird. Maybe Bad GAS or switching brands too often. Why would this thing be detonating with just a CAI? On any of the vehicles that I've had I've never seen a CAI cause Detonation but maybe im wrong.

I've had the intake on since last monday and it wasnt doing it all last week or this weekend when I went to the track. I'll try that octane booster stuff tonight and see what happens.

Also It only ever does it under load. If i rev the car to the same RPM range in neutral its got no rattle. It almost sounds like a heat shield rattling against something. Im really thinking bad gas at this point, good thing shes almost empty, Im going to head to BP instead of sunoco this time and see if that solves the problem.

**Justin93** · 07-16-2008, 12:33 PM

another Idea I just had was since this is at only high rpms could this be a sign of clutch or flywheel wear being GM in its infinite wisdom didnt exactly put the best clutch systems in these cars. Ive heard of guys having High rpm rattles due to this.

Ive also noticed today that it is most audible in second gear going to third and the shifts get really difficult when racing. Also I have noticed that it will make the same noise when im in a numerically higher gear going at a real slow speed causing the motor to bog down. I think this just might be a random rattle after doing some more trouble shooting.

**INMY01TA** · 07-16-2008, 07:39 PM

Could be anything.

**wultdat** · 07-16-2008, 07:58 PM

I have the same problem and I think it's detonation. Like you said it will also do it if you are in a higher gear at a low RPM. One thing I noticed is that it won't do it every time I give it gas. Usually after I do it once it won't do it again if I try about one second after that; but if I wait several seconds and then do it again it will do it. So I don't think it is something physically rattling otherwise it would do it every time. At least in my case.

**INMY01TA** · 07-16-2008, 08:12 PM

Get Autotap and see if you're getting any KR. Great tool to have.

**Justin93** · 07-17-2008, 09:41 AM

Well I drove it all last night and today on a new tank of gas from BP and no rattles at all, Im at a loss lol. I guess it fixed its self.

also where can i get this auto tap scanner? anyone have a part number or model number?

**Spaz** · 07-17-2008, 10:04 AM

if you just had your cats replaced they could have bent or bumped a heat shield that it vibrates... the tones and frequncies and everything else might make them vibrate more at that rpm range than others...

**Justin93** · 07-17-2008, 03:04 PM

Originally Posted by Spaz

if you just had your cats replaced they could have bent or bumped a heat shield that it vibrates... the tones and frequncies and everything else might make them vibrate more at that rpm range than others...

I was in pittsburgh on sunday and did bottom the car our pretty good on the drivers side and noticed scraping on the y pipe. Something must have broke loose causing this rattle cause now it rattles all the time.

update it seems the drivers side heat shield on the manifold was loose after further inspection and needed tightend. I could duplicate the rattle by tapping on it.

**INMY01TA** · 07-17-2008, 03:28 PM

Originally Posted by Justin93

also where can i get this auto tap scanner? anyone have a part number or model number?

http://www.autotap.com/
http://www.thunderracing.com/catalog...vid=3&pcid=152

**Spaz** · 07-17-2008, 03:49 PM

Originally Posted by Justin93

I was in pittsburgh on sunday and did bottom the car our pretty good on the drivers side and noticed scraping on the y pipe. Something must have broke loose causing this rattle cause now it rattles all the time.

update it seems the drivers side heat shield on the manifold was loose after further inspection and needed tightend. I could duplicate the rattle by tapping on it.

easy fix!!!! hope that was it!!!

**Justin93** · 07-17-2008, 03:56 PM

Originally Posted by Spaz

easy fix!!!! hope that was it!!!

I just ran it down the highway hard and had zero rattle, I hope that was it too lol.

**0rion** · 07-17-2008, 05:53 PM

yeah, hope so. It's hard to diagnose this sort of thing over the internet. I just read through your posts again and would've swore this was detonation from the descriptions you were giving.

**Justin93** · 07-17-2008, 07:27 PM

Originally Posted by 0rion

yeah, hope so. It's hard to diagnose this sort of thing over the internet. I just read through your posts again and would've swore this was detonation from the descriptions you were giving.

Thanks for the trouble shooting help anyway. Ill keep this updated but so far so good

**qwkgto** · 07-18-2008, 12:58 AM

Originally Posted by Justin93

Thanks for the trouble shooting help anyway. Ill keep this updated but so far so good

always better safe then sorry.

**Justin93** · 07-18-2008, 12:08 PM

yea Ill be a quaker city raceway tonight making a few passes, we'll see what happens

**Justin93** · 07-20-2008, 12:28 PM

We'll two tanks of gas later and a night of hard racing plus city driving and no issues, Im thinking it was either the gas at the sunoco station or it was the heat shield. Either way Im much happier now.