Creaking CATs

Greed

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.