The brace you are looking for is the black brace that is near the rear-center of the car. You can see it really well in this pic (found online). There are (4) bolts that attach the front of this brace that can have washers added to give the exhaust more clearance in this area.
I personally used (3) stainless fender washers under each of these bolts this weekend, and it made a HUGE improvement in the rattle issue I was having. I honestly think my Ark DTS was resting on this brace slightly after I added Berk HFC's. It rattled a ton and basically sounded like crap until I added the washers. Now I love to drive my car again!
