my formula has a 5.0 TPI and at idle speed, it will make a funny rattling noise....this noise comes and goes, so i can't really pinpoint it......i think it may be a pulley, but i don't know....does this sound familiar to anyone b/c it's driving me crazy

 

My Z started doing the exact same thing a few weeks ago. I would also appreciated it if some one had any idea what this could be.

 

Where does this rattling appear to be coming from, you said the pulley but I'm not sure if a pulley would rattle. Look for anything that is loose or could wiggle around that area to make the noise. Also check under the car near you exhaust to make sure nothing is loose around it.

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

 

you should check your cat. sometimes when the catalyst inside breaks up or its old it will rattle. mine does, but its going to out of there soon.

 

where is the rattling noise coming from? is it loud? take a length of hose and try to pinpoint where the noise is coming from. a rattling noise that i ran into was coming from a bad PCV valve. good luck

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88' IROC-Z, 350 TPI, 700-R4

 

If you think it's a pulley, then just run your motor with the belt off for a few seconds and see if the noise continues. Don't leave it running like that though.

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-Dan
-1990 3.1L RS
-Mods? no
-Slow? yes
-Currently collecting parts for T5 swap

 

Are you running the AC? My IROC rattles (seems to be the spark plug heat shields) when the AC is on (till the 134a runs out anyway). The rattle comes and goes, it's not constant, but never there unless the AC is on. I'm wondering if the clutch bearings might be bad on the compressor, but haven't had time to check it yet.

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Z's r Best

 

i thought mine was rattling from under the hood, but i started it and listened, and turned out to be my cat. now i have a new muffler on and i can't hear the rattling cause its so loud.

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- David
88' GTA 350 MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT

 

I don't know about the other guy, but mine seems to be coming from somewhere other than a pulley. It seems to be coming more from the back of the motor. I know it isn't the cat because I don't have one. I also don't have AC. I know it isn't the alternator because I tried another one. I'm pretty sure it isn't the water pump. If it was an exhaust leak I would think you would hear it all the time.

 

Well, I used to own an '84 Z28 with an auto tranny. It's been a while so I'll try to remember as best as I can. There was a noticeable rattling at idle(I believe when the trans was in gear), especially when the car started to move. Once the car was cruising the sound would disapear. It turned out to be one of the torque converter-to-flywheel bolts. It worked itself loose and would rattle under load. Once cruising the sound would disappear because there wasn't as great a load being placed on it(bolt) when compared to accelerating. This could be what you are experiencing. Just a guess though.

 

For the longest time, I had a strange rattle around the bellhousing area, at idle for the first 30 sec. or so, intermittent. Finally figured out it was a cracked flexplate (the flywheel on auto trans cars), fifty dollar part, one hundred sixty labor. The B&M flexplate is around a hundred, and thicker, but I think weighs more too. Anyway that fixed it. I have another small rattle and that is the power steering pump, but my mechanic said no need to fix. Engine revs totally smooth now, before had a bit of a "wobble" because of the flex plate. My .02.

P.S. I changed the tranny mount and motor mounts before figuring it out.