I would look at the cat bracket, like mentioned above. A lot of people, including myself, have just taken them completely off. they crack and then they can rub and rattle at specific RPM's. Its an easy, free thing to try.
'14 Tuxedo Black ST3
'13 Ingot Silver Escape Titanium AWD
'04 CD Silver SVT, #877, 1 of 135 May 2011 ROTM, FF11: Best Display, Best of Show; AFN12: Best SVT, Best Audio, Finest Five, Carlisle Nifty Fifty