Annoying Rattling

PG370

ok i am about o kill myself from the rattling coming from my exhaust. I have the stillen exhaust which i ha dinstalled on my stock cats, recently i got the Berks which i love, great sound and power but idk if its the cats or what but after i installe dthem i was having a rattling noise. I took the car back to where i had them installed and it seemed that the hfc's made the y pipe on the stillen exhaust hang lower and rattling against a chassis support there is down there, fine i had them use a crowbar to push the y-pipe up a bit and problem solved, or so i thought. Then, when i would go over certain bumps on the street the y pipe would hit it and make a rattling noise again so i ended up buying thermal wrap and warapping it around the area that was rattling to make it tight against the chassis support which worked fine at first but there is STILL something rattling down there sometimes and its driving me nuts. Could there be a heat shield or piece of metal hitting the exhaust, has anyone else had this problem, its seriously killing me and i want to figure it out. Any suggestions would be appreciated. Btw i have looked under the car while it is on and i cant see anything rattling due to when the car is in idle it never rattles so i have no clue.