Hello everyone, this is my first post on here so I thank you all in advance for your assistance. I recently (3K miles ago) purchased a 2003 Trailblazer LS 4WD with about 150K miles. When accelerating from a stop, it sounds and feels like something large is sliding around in the rear of the truck. I hear a loud clunk-like noise and it feels as though something large slid to the back of the truck. Yesterday I was changing the rear brakes, and behind the front part of the rear passenger side wheel, I noticed a split in what looks like part of the frame (please see the attached photos. So I grabbed the rotor and pulled it forward towards the front of the car and backward towards the rear, and sure enough it is making the noise I hear when accelerating. Also, the gap that is in the split seen in the photo is opening and closing. I'm having trouble figuring out what this part is and whether or not there is a prefabricated part that I can purchase to either bolt or weld on. Thank you all for your help.