Creaking CATs
 

I had new Berk HFC's installed on my Z about 10 days ago. I already had the Stillen CBE installed and I am very happy with it. The Berks added even more power and torque (butt dyno only) and improved the exhaust note quite nicely, even if it is a bit loud for my taste now. Overall, however, I am a very satisfied customer.

My issue is this: Since I had the HFCs installed, I can hear a dull, metallic, creaking sound coming from underneath the engine bay when my car is cold. After the engine fully warms up (about 10 minutes of driving), the creaking sound vanishes completely.

Anyone else experience this? If not, does anyone have any ideas what might be causing it? Should I be concerned? I suspect it has to be the CATs b/c I heard no creaking sound before I had them put in.

Is your Z a 6MT? Listen to TheDreamerz car at start up....I'm not sure if this is the sound that you are referring to, but If it is, this is normal...as I too hear this on my Z when I first crank it up on cold start...and this is with a stock exhaust system....You will begin to hear this noise after you release the clutch....You probably hear it more so now then before being that your exhaust system is a lot louder.....

Thanks for the response, Bolio. I'm at work right now so I can't watch any YouTube but I'll check it out when I get home. My car is 7AT.

I listened to the video and that's not the sound I am hearing. Its more like the sound of metal slowly expanding or stretching, like the sound of a metal door opening slowly, or like the sound you hear in the movies when some of an elevator's cables have broken and the remaining cable is straining to support the cab.
I spoke to a tech with Berk and he said its nothing to worry about, so long as the sound goes away when the car warms up. He said the sound was likely caused by the ECU doing it everything it can to warm things up as quickly as possible.
My car is running great and I have no CEL so maybe I shouldn't worry about it. The noise isn't very obtrusive and doesn't last long. If I was listening to the stereo I would never notice it.