Whats it mean if when you turn your car on and it start to make a rattle noise at idle, but the noise goes away while pressing gas, but comes back during idle? And it lasted only the first few minutes of it idling, I guess after it hit operating temperature it went away (although it does come back again a little here and there during idle). The noise came from underneath the car, possibly the exhaust. The car has cat back flowmasters, do these make noise usually, while idling after a cold start? Is it the exhaust? Is it common, no big deal?

Any help is appreciated, thanks.

 

broken cat? part of cat in teh flowmaster?

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-Tas
'89 Formula WS-6

305, TBI, 700R4, P.A.W. 14x3 open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips, Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248)
Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options

 

most likely ur cat...
go under your car and hit it, just use you're hand, or tap it with a hammer (WHEN ITS COLD!!!) when you hit the cat it should making a rattling noise...
i had the same problem, and thats how i figured out what it was.

btw, don't burn your hand!

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1989 G92 Iroc 305 5spd 3.45 posi
mods: airfoil, MAF screens, flowmaster 80's, K&N's, TES headers, Catco hi flow cats (dual of course).

Other:
Tints, Eclipse CD8051 HU, Nakamichi pa504 (50x4 watts), Polk 4x6's, Polk 6x9's, Xtant 1001x amp (1000 watts), 2 xtant X-series 12 inch subs= people know i'm comin' a block away

Just ordered these (at midnight b/c i'm an idiot): Taylor Spiro Pros(8mm), and an MSD Blaster coil

Soon= ram air, ported intake, cam, ignition

 

mine was making a kinda of rattling noise when first started, really loud, turned out the two bolts that bolt it to the y-pipe were loose.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series Muffler added to Unkown CatBack, Ported Intake

http://www.geocities.com/david_angel_16

 

Mine would make a rattling noise at idle too, it was a Catco cat.. but, the rattle was annoying, so I just pulled it

It could also be the heat shield that bolts to the undercarriage.

-Roshambo

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-Joe
1988 Pontiac Trans Am WS6 - 305 TPI, 700R4, 3.23 Posi, Digital Dash, Leather Seats, Maui Blue with Silver GFX, T-tops, Tinted Glass, Gutted MAF, TB Coolant Bypass, K&N Cone Filter, No Cat, 3" exhaust from Y-pipe back, MSD Super Coil, Accel 8mm wires, L98 Aluminum Heads, Ported and Polished Plenum, Siamesed Intake, Aluminum Driveshaft, Edelbrock 3 point Strut Tower Brace