Careful moding the cats is a felony violation of the Federal Clean Air ACT and is an excellant legal reason to void the engine warranty.

 

I have not modded any HFC...Its legal and is designed to still pass emissions. This is the reason why i bought them. I have ran it by Firestone and they told me that its def internal such as a lifter or valve thats getting stuck.

 

Actually it's illegal to replace operating cats with aftermarket cats if the OEM cats are still under the emissions warranty which usually lasts until 80-90K miles.

BTW, your noise is not being caused by a bad lifter or valve. If that was the case, you're motor would be down on power and driveability would be pretty poor. Most likely the noise culprit is the significantly thinner walls of the HFCs allowing more exhaust/valve noise out through the casing.

 

OK, so I have several statements and questions.

1) You say noise through the casing, of the cats or engine?

2) It only becomes noticable once the car has been driven for several minutes.

3) At startup I cannot hear any tapping.

4) It does not sould like all valves or lifters making the noise, only one.

5) When revving the engine you cannot not hear it tapping.

I am gauging this on my OLD days when a valve job was needed, it tapped all the time, hot or cold, idle or revved up.