Brassy noise coimg from exhaust when accelerating and power response delayed after shifting and is worse when the a/c is on. Might have to have catalytic converter replaced and was wondering if this is covered under the 5yr/100,000 miles drivetrain warranty and if it is, would I have to pay labor costs if I bring my car to a pontiac dealer?

Could be the exhaust heat shield has come lose from rusting over the years. Without more diagnosis it is hard to tell what the noise is. What i have suggested is just a common rattle from under the car. Need more to diagnise effectively

sleeve the break with oversised pipe see if it runs ok then -if so -cheap fix

Have you had fuel pressure tested, as well as exhaust for possible plugged catalytic converter?

get it looked at, noise is a hands on deal.
and can be dangerous to drive, to you , the engine (or?) and public.
get it diagnosed, (location of noise is first)

engine worn out, bearings, lifters, cam, intake & exhaust valves , valve guides, all BAD !!!!! SOME MORE THAN OTHERS ! maybe i'm wrong ?

SOUND LIKE LOW COMPRESSION.EXCESSIVE CARBON INSIDE ENGINE CAUSE ENGINE TO DIESELING KEEP RUNNING MAKE A RATTLING NOISE WHEN YOU TURN OFF IGNITION.

The main problem with accents is the front exhaust pipe from the manifold, it has a 90 degree flexible pie that looks like steel wool......if you look down from the top of the motor down, you can just see the exhaust shield covering the manifold, and if you trace it down, you can see the very sharp bend. As it ages, the steel woven mesh becomes loose and creates this rattle buzz noise that is very annoying, and becomes worse on acceleration. Unfortunatley it needs to be replaced. No easy fix, unfortunatley.

I hope this is helpful, let me know if any more questions.

PLease vote if you liked this response. !!!!

I'm wondering if you could have a burnt exhaust valve cause by the exhaust leak in the cylinder where the exhaust leak was.

Hi,

Thanks for using Fixya.

One of the most common complaints with automatics is fluid leaks. Fluid can leak out of the driveshaft seals, the input shaft seal, the transmission pan gasket, the torque converter or the ATF cooler and line connections. If the fluid level gets low, the transmission may be slow to engage when it is shifted into drive. Gear shifts may be sloppy or delayed, or the transmission may slip between shifts. If the fluid level is really low, the transmission may cause the vehicle to not go at all. I hope this helps.

Thanks and have a nice day.

- Hotratchet

A small exhaust leak can sound like a ticking noise during acceleration and can get better or worse as the system heats up. I had a similar problem when the engine was cold that was solved with a new exhaust manifold gasket.