I also have this same problem, it started when I installed my FI HFC, noticed it pretty much the next after i put them on. This seems to be a common thing with our cars.

 

I think its normal but correct me if I am wrong.

 

I don't know if this helps but I've posted my exhaust note before w/hfc &
w/o hfc and you could hear this sound with HFC at the end of last rev.

With HFC
http://s355.photobucket.com/albums/r...rent=FIHFC.flv

without HFC
http://s355.photobucket.com/albums/r...t=MOV01620.flv

 

The sound is normal...

 

yup normal... I was told by a top VQ tuner that all VQs make that noise... different exhausts amplify it a lil and certain exhaust silence it more than others....

 

That is really weird. I just might have to get a different exhaust or remove the HFC's cause it's driving my nutz!

 

Where is it driving your nutz? lol

 

I have a rattle as well from the heat shield, but mainly at cold start. I heard that infiniti circulated a bulletin about this but has yet to issue a recall. Either way, they are aware of the problem and it's not uncommon.

 

My guess is with the less restrictive CAT's your hearing VVEL at work, going back to stock cats would resolve the issue.

 

You're getting a slight resonance from the combo of HFC's & the exhaust. The point where it resonates will vary as you change exhaust components. If you had a different exhaust, the resonace may move up or down in RPM, or disapear altogether. But it's completely normal.

 

I guess i could learn to live with it.

got a ? for you all at berk. How come your HFC dont come with gaskets?

 

We're the only manufactuer that include a set of gaskets for the OEM header/cat connection. Depending on when you bought them, they are either copper or soft crush graphite. The newest ones are the soft crush graphite gaskets.

 

I didnt have any in my box so i reused the stock. How can a get a set from you?

 

Which gaskets? The 2 bolt or 3 bolt?

 

I could use both if you have them