Audi Newb, help!

[SlappyB6]

Okay, I posted this on another forum, but have gotten no replies after almost a week. Anyhow...

Recently purchased a 2002 A4. Love the car, but I'm having some issues. One, I have a CEL. I work at a dealership, had them read the codes and got the wonderful P0420 code. So naturally I need to replace the cat. Any good aftermarket ones for not a lot of money? The dealer has agreed to pay for repairs as long as I can keep the cost under $700.

Second problem. I hear kind of a "whomping" noise when driving. It seems like it's coming from the rear end, and it increases with speed. It also is much more noticeable at lower speeds. I was thinking it was an off-balance tire, but then I started to see a lot of what looks to be dirt and grease on the back tires. So now I'm thinking bad CV boots? Or could it be something else?

Thanks for any and all input!

[AudiA4Turbo22]

1.) a high flow cat would be a good idea! probably $200 or a testpipe if u don't mind a bit more noise $100

[SlappyB6]

I thought about a test pipe, but I have emissions to worry about here in NC. Is there a way to "deal" with that?

[kolan67]

high flow cats are only $200?

[mxrz]

High flow cats provide about 0whp gain.

[AudiA4Turbo22]

^^forget it then!

[kolan67]

Why the hell is it called a "high flow" cat then if theres no gain?

[jrau13]

It just has a lower cell count which is supposed to be "high flow" but they aren't any better or worse than a tp. You wont get the sound of a tp and they are generally a lot more than $200.

[jrau13]

You could always get the test pipe then when emissions time rolls around reinstall the cat.

[SlappyB6]

My inspection isn't due until December. I was thinking getting a test pipe with a full exhaust, and then eventually order a cat and just throw it on when I have to get my inpsection.

And ideas on the other concern? The brakes feel fine, and I don't notice any other concern besides the noise. And the noise seems to get louder after I drive a while, and then slow down. So I'm thinking it might be the CV boots, and once everything gets heated up, that's why I tend to hear it more at certain times?

[gdawg'05a4]

If your car has less than 80k miles/8years, the cat should be replaced under the federal emissions warranty...unless you want to go aftermarket.

http://www.epa.gov/obd/warranties.htm

[SlappyB6]

Oh, I'm quite aware of that. But my A4 has 109K miles on it right now. I appreciate the info though.

[gdawg'05a4]

D'oh. No problem!

[grimlock]

Btw, Techtonics Tuning sells a HFC for $350 I think. Not cheap, but it's definitely less than $700.

[SlappyB6]

I was thinking of doing this:

I want to get an exhaust, and I have a local shop that I've had 3 previous vehicles to, and they do damn good work. I'm going to buy the test pipe, have them install it and do the exhaust, and get the stealership to pay for whatever. Then at some point before December I'll pick up a new cat to install for emissions.

As for the other problems, I'm still at a loss. I guess I just need to pop the back wheels off and see what I can see.