Exhaust Rattle on Start Up
 

I recently installed the HKS Hi-Power CBE and Berk HFC. I did the exhaust 2 weeks before the cats. For those 2 weeks, everything was fine and I was getting no weird noises. After the cat install, most of the time when I start my car now I get a pretty loud rattle coming from the back end of the car. After the car runs for about 30 seconds, the rattle goes away and doesn't come back again until after I let the car sit for a while and come back out and start it up again. Does anyone have any ideas what this might be?

Did you remove the emission canister shield?

I'm not sure what that is honestly.