Any Gen 5 Camaro has a OEM quirk that Holden identified in 2000 but never fixed. The rear suspension moves at it's attachment points on the chassis a tiny bit. A little more as time goes by. Why? The chassis is not sufficently rigid oem. A piece of 2" diameter exhaust pipe goes a long way toward improving this issue without any negative effects. Along the floor in the trunk measure the exact distance between the bottoms of the wheel wells. Cut the pipe a little longer and force the pipe inbetween the bottoms of the interior wheel wells. 2" pipe spreads the contact points more than enough for it to be strong but not rip into the wheel well. A slight angle cut helps too. The car does not need a rear shock mount brace when the oem chassis is pre loaded just a tiny bit. The attachment point is plenty strong enough but the chassis does flex there oem. Not after doing this.