My exhaust has been making an awful rattling noise at cold startup for awhile now. It calms down when the car warms up and you can't hear it while the car is driving...only when it starts up. It sounds like its coming from the downpipe. I'm running a catted zzp 2.5 downpipe with mid length header for over a year. I heard the this setup could rub against the heatshield. Anybody have any similar issues with this setup?