The problem: It "CLATTERS". It sounds like a license plate in a blender.
It used to do this only when in drive. and would go away when in neutral.
Now, it does it right at start-up, and never quits. In every gear , including "park".

The facts: It is a 1989 Chevy S-10 Blazer,
4.3 liter engine.
Automatic
4X4

Mileage: "More than countable"

More info: The previous owner took it to at least 5 different shops to be diagnosed, and nobody has come up with an answer. There are receipts in the glove box stating how all sorts of things have been checked, to no avail.
They say it is NOT the valve train, the water pump, the alternator, the torque converter, or the transmission.

The best advice that has been given, it to "just drive it till something falls off... then you'll know what it was!"

ANY IDEAS?

THANKS, in advance!

~Meat

 

Does the sound increase with RPM?
Where is it coming from? Engine bay or under the truck?

Im going to take a wild guess without knowing the above and say its your catalytic converter. When mine went bad it made a rattling noise, and sometimes the heat shields come lose on them and make a really bad rattling noise.

 

Heat shield?

 

That's what I was thinking. I have seen it a ton on numerous other types of vehicles.

 

Could be the flywheel where it bolts to the crank. Ive seen where they would break around the flange and keep going but sound like hell. But I would look into hitting the catalytic converter with a rubber mallet and see it it rattles first.

 

that would be my guess, but i would think any mechanic would have been able to figure that out. had a 04 suburban come into work, same thing, something banging underneath. owner thought it was the flywheel dust shield rubbing cause it has that thin metal banging against something sound. inside converter blew up and is rattling all over the place.

this truck had the catalyst insufficiently code though which was a dead give away

 

Going along the converter route & seeing that it was only in drive, then eventually all the gears including park & neutral. That could make sense because as something comes loose it will rattle or vibrate at different frequencies. As the piece gets looser it takes less of a specific frequency for it to rattle. It's all about the harmonics of it.
Like it may only rattle if you revved it in park on the down slope of the rev instead of the upward slope of the rev. Same goes with the engine load in gear or not - it'll vibrate differently until the piece eventually breaks & then just bounces around inside the cat.
I'd also take out the inspection plate on the bell housing & take a look inside, rotate the engine by hand & look at the flywheel all the way around it.

 

UPDATE: I got under it today, and the sound doesn't seem to be towards the rear, far enough to be the CAT.
It DOES however sound like it is coming from the area between the engine and the trans. Flywheel?
The engine speed has NO effect on the rattling noise.
UUGH.... what a pain.
Would give up a few toes to own a hoist! (can't give my left ARM, I NEED IT)

 

I had a rattle that i could not locate. It turned out to be something ratteling in the heater core. Pinch off the heater supply hose while reving it up and see if the rattle diminishes. I replaced my heater core and no more rattle. I thought it was the cat or something in the exhaust or a cracked flex plate. None of those were the issue.

 

Torque converter cover or brackets loose/missing a bolt?