Flummox,
You have an aftermarket bar on your car. Chris put on the SCA 21mm bar, not sure if he swapped it out for the stocker, but easy to tell.
Stocker is black, SCA is raw aluminum color.
Dealership should refuse your warranty claim, provided it is still under warranty.
I would order a set of 21mm Type A brakcet/bushings from ProThane and drop use the factory bolt to hold it up and then use a 1/4 thick 1" long bolt with plenty of large washers up top and on bottom and drop that down the stock hole that the brakcet lip fits in.
You can buy another factory bracket but it will only last a few weeks/months before the clunk is back!!! Factory brakcet is about $8 and takes about 5 minutes to install once you have rear end off the ground.
