This is my first post in a long time so bare w/ me.

1) ENGINE RATTLE-- My engine makes a rattleing sound only under higher rev. Around 2700-RPM. It only does this under accelleration. Other posts note similar problems, but most of them have rattle all of the time. Another thing...It sounds like it is coming more from the bottom of the engine compartment. I have a rebuilt tranny, so I hope it is not that.

2) HESITATION-- Again I have seen similar posts, but the details seem different. When I get in the car and start it cold. It starts fine. But when I go to pull out of my driveway or work. Anywhere that I need to accellerate pretty quickly. The car hesitates and sort of stalls. It doesn't turn off. After a few seconds of this it will come back and go like normal. The Engine will rev and then bog down. It really only does this if the engine
hasn't been run a few hours.

PLEASE HELP...or refer me to a relevent post. Thanks.

Check for loose heatshields, splash guard, etc.


I'm sure you've seen the posts, but try cleaning your MAF, check for vac leaks, and if you haven't already or within the last 10k miles, replace your fuel filter. Those are just some basic things to start with.

You've got the same thing as MooseGundr.
As I told him:

"Happens on accelleration. Check.
Sounds like metal rattling, like tin cans. Check.
Causes stumble or hesitation. Check.
Sound comes from underneath car. Check.

If I were betting cash money, I'd guess plugged catalytic converter. Just take it to an exhaust shop, they can check it out pretty quickly."

We had the exact same thing last fall on my wife'* 2001 Grand Prix GT. Plugged Cat. Best part, there'* a law that makes GM pay for the whole thing if you have under 100,000 miles (in California, at least). If over 100,000 miles, just pay for it and get it done.

But seriously, you can stop troubleshooting it at this point and just take it to an exhaust shop.

And let us know how everything turns out.

Echo SSEi and Moose crawled under the car this weekend. I hear the cat isn't rattling and they need more time to get a better understanding.

You may want to check the Harmonic Balancer on the rattle issue.

Harmonic Balancer will rattle at idle and go away as you accelerate.

Find out if you can duplicate it in your driveway while you watch under the hood. Pay attention to your AC compressor clutch/pulley. Is the sound any different when the AC is on or off? Are your belt(*) and idler(*) jumping or moving?

Do this in neutral to 3000 rpms, then again in gear with the parking brake set and 'power brake' it to the same 3000. Any difference? Or is it only when driving?

If it'* only when driving and not AC dependent, get under the car and inspect the front swaybar endlinks for play.

On the hesetation.
Have you done a standard tune up and cleaned the throttle body, changed PCV, and filters along with fuel injector cleaner?
This is the logical start.

I'm feelin' a bad cat.

I'm not feeling this. A typical cat will act up when the car is up to temp, not cold. Let'* try and diagnose the problems instead of tossing out guesses. I wouldn't want to see this person spend $150 or so on a new cat w/o diagnosing and merit.

I'm not suggesting he throw parts at it, I'm agreeing with previous posts, which also suggest verifying the concern before continuing with repairs. The only other thing that i've seen cause rattling around 3K are bad rod bearings. But that doesn't agree with the hesitation.

When my cat failed, I couldn't rev it above 3K, even in park/neutral. It rattled. It bogged. It did this all the time, not just when it was at a temperature extreme.