Well, I decided to check the cat today. The car was running even worse (couldn't get past 3500RPM)

I think the guy lied to me, it doesnt appear to have ever been changed, right?

Instead of dealing with the rusty bolts, I just took the EGR valve off to see if I could get to even higher RPM and if the ticking/fluttering sound stopped. It did both, which leads me more to believe its the cat. [I plugged the intake side with a socket to not creat a potential vacuum leak]

So, with that U bend, it looks hard to hollow out the cat [for more testing]...is it possible with something? Also, are those bolts threaded into the muffler flange? How could I get them out?

Also, do you reccomend an aftermarket cat that splices in or one with the entire pipe and flanges and U bend?

Thanks guys, very right it seems about the fluttering EGR valve!

It most certainly sounds like congestion in the motor. The cat is my number one suspect if plugs/wires/coils/battery have been checked.

OMG.....Look at the corrosion on those pipes.

You're right...that does not appear to be a new cat. The system does bolt together, and you may be able to get it apart with a lot of PB Blaster and patience. Which one you get is personal choice. If you want better performance, or are considered mods, an aftermarket high flow and getting rid of the U-Bend is considered the way to go.

I've also read through a few times, and missed the part on the ticking/fluttering EGR being an issue.

Thanks guys. Yea I have some aerokroil (better than PB IMO) that I can try to work at those bolts. But I think I am going to check with the dealer to see if I can still make the emissions warranty, if not, I'll just weld in a regular cat b/c I dont need the performance.

Well, I didnt know what was causing the flutter, but since I removed the EGR, that noise was gone leading me to believe the extreme back pressure was causing the EGR to open and close rapidly. I am assuming, it was hard to hear over the exhaust leak I created.

Anyone know if the 2000 was covered under the extended 10yr/120K warranty. I know 2001-2002 was.

Well, here is the follow up!

Clogged huh? What is that stuff? Doesnt make me feel very good about my engine! I'll let you guys know if it runs any better when I install it tomorrow.

Hmmmm.....from the looks of that Cat you may need new pistons soon. Try using a magnet to see if it'* aluminum pieces.

I see you got a shiny new cat, which one did you end up getting? I bought one of the Magnaflow ones, but it turned out to be too big The cat fits in a small area on the W-body and the Magnaflow was just too big too go in there.

Ok I'll try the magnet and I think I will bust the cat up to more closely inspect with this stuff is. If there is metal in it... trade-in?

I just bought the cheapest $54 cat from Advance Auto. Its even smaller than the original one, but the Impala has some room for something bigger. I was going to do the highflow and U bend delete with a Mil faker, but I'm thinking I a newer vehicle even before this, so I just did the legal minimum. The cat is 2.5" in/out. Thanks for the responses!

You can still keep a functional o2 sensor with a high-flow cat and u-bend delete. You can either weld whats called an o2 bung somwhere into the pipe and screw it in there. I actually bought a short section of pipe off ebay that had a bung already in it.

I do occasionally have an SES light related to the cat, but I think its because the wiring is officially crammed up in there and might short or ground out occasionally. It only happens like once every couple months or so.